Format A2DP-related code with clang-format

clang-format -style=file -i stack/a2dp/a2dp_* stack/include/a2dp_* \
        btif/include/btif_a2dp* btif/src/btif_a2dp*

Test: top-level compilation and running A2DP
Change-Id: I66f0a047192b783ac0147def480754daf617dd8d