In the constrained framedrop mode for svc: modify the buffer check
condition relative to (non-zero) dropmark to include uppper spatial layers,
in addition to the current spatial layer.
But keep the single layer check if the buffer goes below zero, since
in this case (buffer underflow) we should force drop of that layer
regardless of upper layers.
Change-Id: Id277f0b4a3ae6275effdd5f5f0c80e3229c17424
e358cf0a43