Merge bitcoin/bitcoin#21710: doc: update helps for addnode rpc and -addnode/-maxconnections config options

b4fcbcf doc: update -maxconnections config option help (Jon Atack)
79685a8 doc: update -addnode config option help (Jon Atack)
2896c6c doc: update addnode rpc help (Jon Atack)

Pull request description:

  Since #9319 proposed by Gregory Maxwell and released in v0.14, peers manually added through the `-addnode` config option or using the `addnode` RPC have their own separate limit of 8 connections that does not compete with other inbound or outbound connection usage and is not subject to the limitation imposed by the `-maxconnections` option.

  This PR updates the `-addnode` and `-maxconnections` config options and the `addnode` RPC help docs with this information.

  `-addnode` config option help
  ```
  $ bitcoind -h | grep -A5 addnode=
    -addnode=<ip>
         Add a node to connect to and attempt to keep the connection open (see
         the addnode RPC help for more info). This option can be specified
         multiple times to add multiple nodes; connections are limited to
         8 at a time and are counted separately from the -maxconnections
         limit.

  $ bitcoind -h | grep -A3 maxconnections=
    -maxconnections=<n>
         Maintain at most <n> connections to peers (default: 125). This limit
         does not apply to connections manually added via -addnode or the
         addnode RPC, which have a separate limit of 8.
  ```

  `addnode` rpc help
  ```
  $ bitcoin-cli help addnode
  addnode "node" "command"

  Attempts to add or remove a node from the addnode list.
  Or try a connection to a node once.
  Nodes added using addnode (or -connect) are protected from DoS disconnection and are not required to be
  full nodes/support SegWit as other outbound peers are (though such peers will not be synced from).
  Addnode connections are limited to 8 at a time and are counted separately from the -maxconnections limit.
  ```

ACKs for top commit:
  prayank23:
    ACK bitcoin/bitcoin@b4fcbcf
  jarolrod:
    ACK b4fcbcf

Tree-SHA512: b6d69baa6cbf6d53f91bac5b39b549d49db6c95f92ea1bdd3588a6432794a25ac2c8b3c89e2c72bb9097e61f2717c8b5ecc404745d5992b88e523db03200898f

Author: laanwj

src/init.cpp

@@ -420,7 +420,7 @@ void SetupServerArgs(NodeContext& node)
                  " If <type> is not supplied or if <type> = 1, indexes for all known types are enabled.",
                  ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 
-    argsman.AddArg("-addnode=<ip>", "Add a node to connect to and attempt to keep the connection open (see the `addnode` RPC command help for more info). This option can be specified multiple times to add multiple nodes.", ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::CONNECTION);
+    argsman.AddArg("-addnode=<ip>", strprintf("Add a node to connect to and attempt to keep the connection open (see the addnode RPC help for more info). This option can be specified multiple times to add multiple nodes; connections are limited to %u at a time and are counted separately from the -maxconnections limit.", MAX_ADDNODE_CONNECTIONS), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::CONNECTION);
     argsman.AddArg("-asmap=<file>", strprintf("Specify asn mapping used for bucketing of the peers (default: %s). Relative paths will be prefixed by the net-specific datadir location.", DEFAULT_ASMAP_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-bantime=<n>", strprintf("Default duration (in seconds) of manually configured bans (default: %u)", DEFAULT_MISBEHAVING_BANTIME), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-bind=<addr>[:<port>][=onion]", strprintf("Bind to given address and always listen on it (default: 0.0.0.0). Use [host]:port notation for IPv6. Append =onion to tag any incoming connections to that address and port as incoming Tor connections (default: 127.0.0.1:%u=onion, testnet: 127.0.0.1:%u=onion, signet: 127.0.0.1:%u=onion, regtest: 127.0.0.1:%u=onion)", defaultBaseParams->OnionServiceTargetPort(), testnetBaseParams->OnionServiceTargetPort(), signetBaseParams->OnionServiceTargetPort(), regtestBaseParams->OnionServiceTargetPort()), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::CONNECTION);
@@ -433,7 +433,7 @@ void SetupServerArgs(NodeContext& node)
     argsman.AddArg("-forcednsseed", strprintf("Always query for peer addresses via DNS lookup (default: %u)", DEFAULT_FORCEDNSSEED), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-listen", "Accept connections from outside (default: 1 if no -proxy or -connect)", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-listenonion", strprintf("Automatically create Tor onion service (default: %d)", DEFAULT_LISTEN_ONION), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
-    argsman.AddArg("-maxconnections=<n>", strprintf("Maintain at most <n> connections to peers (default: %u)", DEFAULT_MAX_PEER_CONNECTIONS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
+    argsman.AddArg("-maxconnections=<n>", strprintf("Maintain at most <n> connections to peers (default: %u). This limit does not apply to connections manually added via -addnode or the addnode RPC, which have a separate limit of %u.", DEFAULT_MAX_PEER_CONNECTIONS, MAX_ADDNODE_CONNECTIONS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-maxreceivebuffer=<n>", strprintf("Maximum per-connection receive buffer, <n>*1000 bytes (default: %u)", DEFAULT_MAXRECEIVEBUFFER), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-maxsendbuffer=<n>", strprintf("Maximum per-connection send buffer, <n>*1000 bytes (default: %u)", DEFAULT_MAXSENDBUFFER), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-maxtimeadjustment", strprintf("Maximum allowed median peer time offset adjustment. Local perspective of time may be influenced by peers forward or backward by this amount. (default: %u seconds)", DEFAULT_MAX_TIME_ADJUSTMENT), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);

src/rpc/net.cpp

@@ -277,7 +277,9 @@ static RPCHelpMan addnode()
                 "\nAttempts to add or remove a node from the addnode list.\n"
                 "Or try a connection to a node once.\n"
                 "Nodes added using addnode (or -connect) are protected from DoS disconnection and are not required to be\n"
-                "full nodes/support SegWit as other outbound peers are (though such peers will not be synced from).\n",
+                "full nodes/support SegWit as other outbound peers are (though such peers will not be synced from).\n" +
+                strprintf("Addnode connections are limited to %u at a time", MAX_ADDNODE_CONNECTIONS) +
+                " and are counted separately from the -maxconnections limit.\n",
                 {
                     {"node", RPCArg::Type::STR, RPCArg::Optional::NO, "The node (see getpeerinfo for nodes)"},
                     {"command", RPCArg::Type::STR, RPCArg::Optional::NO, "'add' to add a node to the list, 'remove' to remove a node from the list, 'onetry' to try a connection to the node once"},