Update Changelog for Flexisip 2.1.5
Update Changelog for Flexisip 2.1.5

(cherry picked from commit f5fc745cdc186b272f655148d10a6f59b48ea8cb)

BelledonneCommunications/flexisip,BelledonneCommunications/flexisip,BelledonneCommunications/flexisip,BelledonneCommunications/flexisip