gobex: Fix ABORT response being discarded

g_obex_drop_tx_queue() in transfer_complete() clears any pending tx,
so the ABORT success response should be enqueued after transfer_complete().

Fixes the following PTS test cases:
- OPP/SR/OPH/BV-27-I
- FTP/SR/OTR/BV-02-C
- PBAP/PSE/PDF/BV-06-I
- PBAP/PSE/PBF/BV-03-I

Fixes: 7a35c12a6ceb ("gobex: Fix segfault caused by interrupted transfer")
Assisted-by: Claude:claude-sonnet-5