kmswebrtctransport: set "allow-repeat-tx" for srtpenc
kmswebrtctransport: set "allow-repeat-tx" for srtpenc

Needed to allow RTP RTX

Change-Id: I750d2fd59cf9bbd8ab4f40f3987d212f8f353230

TribeMedia/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements,shelsonjava/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements