[net_processing] Defer initializing m_addr_known

Use SetupAddressRelay to only initialize `m_addr_known` as needed. For outbound
peers, we initialize the filter before sending our self announcement (not
applicable for block-relay-only connections). For inbound peers, we initialize
the filter when we get an addr related message (ADDR, ADDRV2, GETADDR).

These changes intend to mitigate address blackholes. Since an inbound peer has
to send us an addr related message to become eligible as a candidate for addr
relay, this should reduce our likelihood of sending them self-announcements.

test/functional/p2p_addr_relay.py

@@ -175,6 +175,9 @@ class AddrTest(BitcoinTestFramework):
         # of the outbound peer which is often sent before the GETADDR response.
         assert_equal(inbound_peer.num_ipv4_received, 0)
 
+        # Send an empty ADDR message to intialize address relay on this connection.
+        inbound_peer.send_and_ping(msg_addr())
+
         self.log.info('Check that subsequent addr messages sent from an outbound peer are relayed')
         msg2 = self.setup_addr_msg(2)
         self.send_addr_msg(full_outbound_peer, msg2, [inbound_peer])