GD-Shim: Free BT_HDR after use or callback failure

* Legacy stack always assume the last user of BT_HDR
  will free the structure. Make sure we do this in GD
  shim as well

Bug: 185083624
Tag: #gd-refactor
Test: gd/cert/run

Send a 31MB video
- before this change, RSS increased by 86 MB when 10% (3MB) was sent
- after this change, RSS increased by 37 MB and stabilized, this
  increase is anticipated as the file needs to be cached in RAM

BYPASS_LONG_LINES_REASON: consist with gd format

Change-Id: Ie934e6d4edd7dfc79b4444ce1c13819834f59692