[Asterisk-video] Fix on video codec negociation

[Emmanuel BUU]

Emmanuel BUU wrote:
> Since Asterisk 1.4, I experienced two incorrect behavior in regards 
> with SIP & video support on Asterisk:
>
>     * Calls fail between SIP phone sharing one video codec and
>       distinct audio codec.
>     * 200 OK returns several audio and video codecs
>
More explanation on the last case : if the two SIP phone share several 
video codecs, then the 200 OK issued by Asterisk as answer to the caller 
contains all those codecs instead of containing only the codec 
negociated with the remote party.