basemixer: Remove pads associated with a port when it is unhandled
basemixer: Remove pads associated with a port when it is unhandled

Change-Id: I2b419850aabd28eb575493df0caadf159ad328b6

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