net_processing: thread safety annotation for m_tx_relay_mutex

src/net_processing.cpp

@@ -291,7 +291,7 @@ struct Peer {
         return m_tx_relay.get();
     };
 
-    TxRelay* GetTxRelay()
+    TxRelay* GetTxRelay() EXCLUSIVE_LOCKS_REQUIRED(!m_tx_relay_mutex)
     {
         return WITH_LOCK(m_tx_relay_mutex, return m_tx_relay.get());
     };