[OpenSIPS] SDP codec manipulation

OpenSIPS 1.6 (devel version) provides a new set of functions for SDP codec manipulation: operations for searching the advertised codecs, to remove advertised codecs or the change the priorities between the codecs (moving in top or at the end of the list).

http://www.opensips.org/html/docs/modules/devel/textops.html#id271999