Always restrict the AVDTP MTU for SBC codec to MAX_2MBPS_AVDTP_MTU(663)

Some devices claim they can handle large MTU and large SBC bitpool.
However, they are struggling and eventually over time they
start delaying the "Rcvd Number of Completed Packets" reports.
Now we always limit the payload MTU to MAX_2MBPS_AVDTP_MTU(663) -
with the overhead of (4 bytes L2CAP Header + 12 bytes AVDTP Header)
such packet can fit within 2-DH5 payload size of 679 bytes.

Bug: 34127145
Test: A2DP SBC streaming to headsets and carkit
Change-Id: I2f32becba703d77d36be46158f68b8a9ef3f299a