Integration of the AAC codec for A2DP source

Also:
 - Implemented data fragmentation inside bta_av_data_path()
   that is RTP compatible.
 - Do not use the codec_type when composing the RTP payload type
   per RFC 3016, Section 4.2. That value doesn't have actual meaning
   in the context of the Bluetooth supported codecs, and is ambiguous:
   all vendor codecs map to the same value 0xFF.
 - Updated support function A2DP_BitsSet() so it works for
   up to 64-bit integers.
 - Updated a log message inside l2c_data_write() to print
   packet length and peer MTU on error.

Test: A2DP streaming to AAC headsets
Bug: 30958229
Change-Id: I1b530f1c5c495b8231fd68bed788d4567096683d