Log: debug user cancellation and log warning for rest

The context error with cancel code is typically for user cancellation which
should be at debug level. For other error codes we should display a warning.

Fixes etcd-io#9085

etcdserver/api/v3rpc/watch.go

@@ -140,7 +140,11 @@ func (ws *watchServer) Watch(stream pb.Watch_WatchServer) (err error) {
 	// deadlock when calling sws.close().
 	go func() {
 		if rerr := sws.recvLoop(); rerr != nil {
-			plog.Debugf("failed to receive watch request from gRPC stream (%q)", rerr.Error())
+			if stream.Context().Err() == context.Canceled {
+				plog.Debugf("failed to receive watch request from gRPC stream 11 (%q)", rerr.Error())
+			} else {
+				plog.Warningf("failed to receive watch request from gRPC stream (%q)", rerr.Error())
+			}
 			errc <- rerr
 		}
 	}()