Merge changes from topic "cherrypicker-L56900000957135174:N84400001307540511" into tm-qpr-dev

* changes:
  Fix advertising enable completion callbacks
  Simplify TestHciLayer
  Revert^2 Move TestHciLayer into a separate file
  Fix flagging for L2CAP fix
  Fix infinite L2CAP timeout when ATT is used without GATT clients
  Avoid out-of-order L2CAP CoC callbacks on channel creation