Fix incorrect merge removed mutex

Author: j-berman

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -1013,6 +1013,8 @@ namespace cryptonote
   {
     MLOG_P2P_MESSAGE("Received NOTIFY_NEW_TRANSACTIONS (" << arg.txs.size() << " txes)");
 
+    std::lock_guard<std::mutex> m_check_lock(m_check_tx_request_queue_mutex);
+
     if(context.m_state != cryptonote_connection_context::state_normal)
       return 1;