tc: Change filter error to debug once

Also update the message to be more correct.
Before this commit if there were tc rules that are not of type
flower the log was getting filled quickyl with errors about it
and always appeared to the user when dumping flows from user space.
This commit moves the error to debug and logs it only once.

Signed-off-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Paul Blakey <paulb@mellanox.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

lib/tc.c

@@ -952,7 +952,7 @@ parse_netlink_to_tc_flower(struct ofpbuf *reply, struct tc_flower *flower)
 
     kind = nl_attr_get_string(ta[TCA_KIND]);
     if (strcmp(kind, "flower")) {
-        VLOG_ERR_RL(&error_rl, "failed to parse filter: %s", kind);
+        VLOG_DBG_ONCE("Unsupported filter: %s", kind);
         return EPROTO;
     }