Quiet some warns for protocol errors setting rendezvous points

In https://lists.torproject.org/pipermail/tor-relays/2014-March/004031.html we see a relay operator reporting lots of "Invalid length on ESTABLISH_RENDEZVOUS" errors.

The code in question is in rend_mid_establish_rendezvous():

  if (request_len != REND_COOKIE_LEN) {
    log_warn(LD_PROTOCOL, "Invalid length on ESTABLISH_RENDEZVOUS.");

Seems to me that log_warn should be a log_protocol_warn, since there's nothing the relay operator should do about some client not obeying the protocol.

Are there other log_warns in this vicinity that we should change also? I looked around a bit and didn't see others.