check_rtp: on IP:port errors, log the IP and port

Half of those are obviously zero, but I'd rather print the raw data instead of
adding string constants, even if the condition must always lead to 0.0.0.0:0.

Rationale: I had osmo-mgw listen on 0.0.0.0 and got the error message
  DRTP ERROR endpoint:0x1 destination IP-address is invalid
which didn't convey that 0.0.0.0 is regarded as invalid.

Change-Id: I9e98d464a27038904797c5c10735a98ef5b7b9c3
1 file changed