Fix nsei+bvci not updated on rx UL SNDCP data

msgid2mmctx() was already being called for signalling messages in
gsm0408_gprs_rcvmsg_gb() before calling gprs_gb_recv_pdu(), but it was
not called in sndcp_llunitdata_ind().

Let's move msgid2mmctx() inside gprs_gb_recv_pdu() since we want to
always update the nsei+bvci, regardless of message containing data or
control content.

This commit fixes the scenario where an MS changes to a new cell (PCU)
and then continues transmitting UL data. Prior to this patch, the SGSN
kept sending DL content to the old cell (PCU nsei+bvci) instead of the
new one even after the MS transmitted Ul content fro mthe new cell.

Related: SYS#4909
Change-Id: I2c14e1d65575f54212924f7c5f0a2f4c1b76ec81
3 files changed