Throw an alert when the peer address cannot be resolved during initiation.

src/libcharon/bus/bus.h

@@ -86,6 +86,8 @@ enum alert_t {
 	ALERT_SHUTDOWN_SIGNAL,
 	/** responder authentication failed, no arguments */
 	ALERT_RESPONDER_AUTH_FAILED,
+	/** failed to resolve peer address, no arguments */
+	ALERT_PEER_ADDR_FAILED,
 };
 
 /**