libmsc/transaction: introduce trans_find_by_sm_rp_mr()
According to GSM TS 04.11, section 8.2.3, the RP Message Reference
is a mandatory field for all messages on the SM-RL (SM Relay Layer),
that is used to link an RP-ACK or RP-ERROR message to the associated
(preceding) RP-DATA or RP-SMMA message transfer attempt.
This change extends the transaction state structure with SM-RP-MR,
and introduces a new function for matching transactions within a
given connection by this reference.
Change-Id: Ice47c37ecef4416e65ecee8931d946c915316791
2 files changed