kmsrtpendpoint: link audio (instead of video) pad to fakesink when it is not configured
kmsrtpendpoint: link audio (instead of video) pad to fakesink when it is not configured

Change-Id: I635c135992701701899d03b1841f05402db8c454

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