Lower logging level when failing to register socket watch

The RPC client treats failure to register a socket watch
as non-fatal, since we do not mandate that a libvirt client
application provide an event loop implementation. It is
thus inappropriate to a log a message at VIR_LOG_WARN

* src/rpc/virnetsocket.c: Lower logging level

src/rpc/virnetsocket.c

@@ -1066,7 +1066,7 @@ int virNetSocketAddIOCallback(virNetSocketPtr sock,
                                          virNetSocketEventHandle,
                                          sock,
                                          NULL)) < 0) {
-        VIR_WARN("Failed to register watch on socket %p", sock);
+        VIR_DEBUG("Failed to register watch on socket %p", sock);
         return -1;
     }
     sock->func = func;