BTIF_AV doesn't start offloading while suspending

This is timing issue that upper-layer was asking to pause the stream
which was starting A2DP offloading, but caused an offloading leakage.
This CL checks those suspending flags to fix it.

Tag: #compatibility
Bug: 201396929
Test: A2DP playback manually
Change-Id: I1150160afc2c36f88db84b3566549c9473c2d7b6