nic_router: when freeing a link log it beforehand

So, it can be located more easily when something goes wrong while
freeing a link.

Fixes #2815

repos/os/src/server/nic_router/link.cc

@@ -155,13 +155,13 @@ void Link::dissolve()
 		log("Dissolve ", l3_protocol_name(_protocol), " link: ", *this); }
 
 	try {
-		_server_port_alloc().free(_server.dst_port());
 		if (_config().verbose()) {
 			log("Free ", l3_protocol_name(_protocol),
 			    " port ", _server.dst_port(),
 			    " at ", _server.domain(),
 			    " that was used by ", _client.domain());
 		}
+		_server_port_alloc().free(_server.dst_port());
 	}
 	catch (Pointer<Port_allocator_guard>::Invalid) { }
 }