net_processing: use CNode::DisconnectMsg helper

This is not a pure refactor:
1. It slightly changes the log messages, as reflected in the test changes
2. It adds the IP address to all disconnect logging (when fLogIPs is set)

test/functional/feature_maxuploadtarget.py

@@ -122,7 +122,7 @@ class MaxUploadTest(BitcoinTestFramework):
         assert_equal(len(self.nodes[0].getpeerinfo()), 3)
         # At most a couple more tries should succeed (depending on how long
         # the test has been running so far).
-        with self.nodes[0].assert_debug_log(expected_msgs=["historical block serving limit reached, disconnect peer"]):
+        with self.nodes[0].assert_debug_log(expected_msgs=["historical block serving limit reached, disconnecting peer=0"]):
             for _ in range(3):
                 p2p_conns[0].send_message(getdata_request)
             p2p_conns[0].wait_for_disconnect()
@@ -147,7 +147,7 @@ class MaxUploadTest(BitcoinTestFramework):
 
         # But if p2p_conns[1] tries for an old block, it gets disconnected too.
         getdata_request.inv = [CInv(MSG_BLOCK, big_old_block)]
-        with self.nodes[0].assert_debug_log(expected_msgs=["historical block serving limit reached, disconnect peer"]):
+        with self.nodes[0].assert_debug_log(expected_msgs=["historical block serving limit reached, disconnecting peer=1"]):
             p2p_conns[1].send_message(getdata_request)
             p2p_conns[1].wait_for_disconnect()
         assert_equal(len(self.nodes[0].getpeerinfo()), 1)
@@ -197,7 +197,7 @@ class MaxUploadTest(BitcoinTestFramework):
         assert_equal(peer_info[0]['permissions'], ['download'])
 
         self.log.info("Peer gets disconnected for a mempool request after limit is reached")
-        with self.nodes[0].assert_debug_log(expected_msgs=["mempool request with bandwidth limit reached, disconnect peer"]):
+        with self.nodes[0].assert_debug_log(expected_msgs=["mempool request with bandwidth limit reached, disconnecting peer=0"]):
             peer.send_message(msg_mempool())
             peer.wait_for_disconnect()