Use return condition to stack/l2cap/l2c_ble::l2cble_conn_comp

Also pull in flow execution from l2c back to btm

Bug: 170396407
Tag: #refactor
Test: act.py -tc BleCocTest
Test: ble paired 2 phones
Test: classic paired Bose SoundLink

Change-Id: Ic8aa743376ca7f8a9f0b868dad4a59437af69847