Ensure that the Churn candidates' MID matches the SDP.
Ensure that the Churn candidates' MID matches the SDP.

Fixes https://github.com/uProxy/uproxy/issues/2143

jpevarnek/uproxy,uProxy/uproxy,uProxy/uproxy,uProxy/uproxy,jpevarnek/uproxy,jpevarnek/uproxy,uProxy/uproxy,uProxy/uproxy,jpevarnek/uproxy,jpevarnek/uproxy