fix sdp nego
fix sdp nego

BelledonneCommunications/flexisip,biddyweb/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,gale320/flexisip,biddyweb/flexisip,gale320/flexisip,gale320/flexisip,biddyweb/flexisip,BelledonneCommunications/flexisip,biddyweb/flexisip,BelledonneCommunications/flexisip