res_rtp_asterisk: Allow only UDP ICE candidates.

The underlying library, pjnath, that res_rtp_asterisk uses for ICE
support does not have support for ICE-TCP. As candidates are
passed through directly to it this can cause error messages to occur
when it receives something unexpected (such as a TCP candidate).
This change merely ignores all non-UDP candidates so they never
reach pjnath.

ASTERISK-24326 #close
Reported by: Joshua Colp


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@424852 f38db490-d61c-443f-a65b-d21fe96a405b