improve forked call context to be more rfc compliant
improve forked call context to be more rfc compliant

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