BIP155: include changes from followup discussions

* Increase the maximum length of an address from 32 to 512 bytes and
  clarify that the entire message should be rejected if it contains
  a longer address.
  (from bitcoin#766 (comment))

* Remove a contradiction about unknown address types - "MUST ignore" VS
  "MAY store and gossip".

* Recommend gossiping addresses for networks to which the node is not
  currently connected to.
  (from bitcoin#766 (comment))

* Clarify that the entire message should be rejected if it contains an
  address with unexpected size (e.g. IPv4 address with length 5).

Author: vasild

bip-0155.mediawiki

@@ -78,8 +78,8 @@ This means that the message contains a serialized <code>std::vector</code> of th
 
 One message can contain up to 1,000 addresses. Clients SHOULD reject messages with more addresses.
 
-Field <code>addr</code> has a variable length, with a maximum of 32 bytes (256 bits). Clients SHOULD reject
-longer addresses.
+Field <code>addr</code> has a variable length, with a maximum of 512 bytes (4096 bits).
+Clients SHOULD reject messages with longer addresses, irrespective of the network ID.
 
 The list of reserved network IDs is as follows:
 
@@ -120,10 +120,13 @@ The list of reserved network IDs is as follows:
 | Cjdns overlay network address
 |}
 
-To allow for future extensibility, clients MUST ignore address types that they do not know about.
-Client MAY store and gossip address formats that they do not know about. Further network ID numbers MUST be reserved in a new BIP document.
+Clients are RECOMMENDED to gossip addresses from all known networks even if they are currently not connected to some of them. That could help multi-homed nodes and make it more difficult for an observer to tell which networks a node is connected to.
 
-Clients SHOULD reject addresses that have a different length than specified in this table for a specific address ID, as these are meaningless.
+Clients SHOULD NOT gossip addresses from unknown networks because they have no means to validate those addresses and so can be tricked to gossip invalid addresses.
+
+Further network ID numbers MUST be reserved in a new BIP document.
+
+Clients SHOULD reject messages that contain addresses that have a different length than specified in this table for a specific network ID, as these are meaningless.
 
 See the appendices for the address encodings to be used for the various networks.