* Re-initialise reference layer on a resume.
It is possible for a down track to resume from seeded state.
But, storing reference layer means it is storing something that
is dependent on up track. On a resume, if the up track does not
produce the reference layer, RTCP sender reports will not be sent.
So, remove that up track dependency and re-initialise the reference
layer on a resume.
This could affect A/V sync, but it should not be bad.
But, need to observe the effects.
* min difference of 1