Only affects 2 temporal layer case.
Modified the flags for 2 temporal layers to make
top layer (top spatial, top temporal) a non-reference
frame, conistent with the 3 TL case.
Add mismatch check to the datarate test of changing
svc pattern on the fly, which is test for 2 temporal
layers.
This re-applies the change: 254e2f5501d,
that was reverted in: 658eb1d675.
Change-Id: Ib5fd4a7a0312c0c05329ae75baac480af34b4694
efa786d464