Make bounce_message_queue wait for 100ms for incoming messages

There is possibilty that between c2s process unregistering itself from sm
and terminating, some other process could try to send something to c2s,
which could result in messages to triggering mam/offline hooks, and causing
them not to be stored in any way.

src/ejabberd_c2s.erl

@@ -902,7 +902,7 @@ bounce_message_queue({_, Pid} = SID, JID) ->
 	    receive {route, Pkt} ->
 		    ejabberd_router:route(Pkt),
 		    bounce_message_queue(SID, JID)
-	    after 0 ->
+	    after 100 ->
 		    ok
 	    end
     end.