bssgp: Only call bssgp_tx_llc_discarded if the bctx exists

While this does not happen in real use, and unset btcx can lead to
segfaults in test cases. The other code outside of gprs_bssgp_pcu.cpp
does not depend on bctx being non-NULL:

Sponsored-by: On-Waves ehf
1 file changed