Increase the ip address relay branching factor for unreachable networks

Onion addresses propagate very badly among the IPv4/IPv6 network, resulting
in difficulty for those to find each other.

The branching factor 1 is probably so low that propagations die out before
they reach another onion peer. Increase it to 1.5 on average.

Author: sipa

src/net_processing.cpp

@@ -1481,7 +1481,6 @@ void RelayTransaction(const uint256& txid, const uint256& wtxid, const CConnman&
 
 static void RelayAddress(const CAddress& addr, bool fReachable, const CConnman& connman)
 {
-    unsigned int nRelayNodes = fReachable ? 2 : 1; // limited relaying of addresses outside our network(s)
 
     // Relay to a limited number of other nodes
     // Use deterministic randomness to send to the same nodes for 24 hours
@@ -1490,6 +1489,9 @@ static void RelayAddress(const CAddress& addr, bool fReachable, const CConnman&
     const CSipHasher hasher = connman.GetDeterministicRandomizer(RANDOMIZER_ID_ADDRESS_RELAY).Write(hashAddr << 32).Write((GetTime() + hashAddr) / (24 * 60 * 60));
     FastRandomContext insecure_rand;
 
+    // Relay reachable addresses to 2 peers. Unreachable addresses are relayed randomly to 1 or 2 peers.
+    unsigned int nRelayNodes = (fReachable || (hasher.Finalize() & 1)) ? 2 : 1;
+
     std::array<std::pair<uint64_t, CNode*>,2> best{{{0, nullptr}, {0, nullptr}}};
     assert(nRelayNodes <= best.size());