kmsutils: Just start keyframe request when a flag is marked as discont
kmsutils: Just start keyframe request when a flag is marked as discont

GAP marked buffers are generated to fill gaps, do not indicate that
a keyframe is required

Change-Id: Iba8a4f7293ffcfae65830c65d5b02ad1e85c968f

TribeMedia/kms-core,Kurento/kms-core,shelsonjava/kms-core,ESTOS/kms-core,ESTOS/kms-core,shelsonjava/kms-core,Kurento/kms-core,Kurento/kms-core,Kurento/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,ESTOS/kms-core,ESTOS/kms-core