Initiate SCO after Mode change event

Use case:
1. Connect a headset to AG.
2. Make an outgoing call using headset.

Failure:
SCO connection request is rejected by headset.

Root cause:
AG initiated SCO connection when mode change is pending
on headset. Remote is coming out of sniff and rejected
SCO connection request.

Fix:
AG initiates SCO connection request once AG receives mode
change event. It resolves a corner case where remote failed
to accept SCO connection when initiated in between unsniff
LMP request. Issue is seen with WEP301 headset.

Change-Id: I4ea5d073630320b30f90e6141f4daf25943cca0b