Add api around select fields tL2C_CB::tL2C_LCB::

tL2C_CB::tL2C_LCB::link_xmit_quota
tL2C_CB::tL2C_LCB::round_robin_unacked
tL2C_CB::tL2C_LCB::ble_round_robin_unacked
tL2C_CB::tL2C_LCB::acl_priority

Towards readable code

Bug: 163134718
Tag: #refactor
Test: act.py -tc BleCocTest
Test: ble paired 2 phones
Test: classic paired Bose SoundLink

Change-Id: I392dac8bd8fb33cf8350a7fac1d160595c54ed1c