Adjust the log level in the block sync extension

The score can become smaller because the block sync extension propagates
proposal block.
If the nodes agree on the higher view block after a node propagates a
proposal block, the score can become smaller.

Author: Seulgi Kim

sync/src/block/extension.rs

@@ -444,7 +444,8 @@ impl Extension {
         match self.header_downloaders.entry(*from) {
             Entry::Occupied(mut peer) => {
                 if !peer.get_mut().update(total_score, best_hash) {
-                    cwarn!(SYNC, "Peer #{} status updated but score is less than before", from);
+                    // FIXME: It should be an error level if the consensus is PoW.
+                    cdebug!(SYNC, "Peer #{} status updated but score is less than before", from);
                     return
                 }
             }