re-add siemens MRPCI message, dropped during MSCSPLIT
During separation of osmo-msc from osmo-nitb, sending of the MRPCI message is being dropped.
One was sent during gsm48_handle_paging_resp() (the function is being dropped completely in Change-Id: Id3705236350d5f69e447046b0a764bbabc3d493c osmo-msc.git).
The other in gsm48_rx_mm_serv_req() (since no lchan info is available, sending MRPCI is dropped there).
Find the proper place in osmo-bsc to send the MRCPI messages, so that we don't diminish support for Siemens BTS.
This probably makes the most sense once the new AoIP code has settled.
The proper solution was implemented in 8156494f36e2ef8f388aeb698baf964b5e3eb349 (not in master), which sends it after ASSIGNMENT COMPLETE and HANDOVER COMPLETE. We could probably also send it immediately after activation of a lchan.
The key aspect is that we need to know CLASSMARK 2 in order to encode the MRPCI message. OsmoBSC currently doesn't keep this information stored anywhere. So we first need to store CM2 as part of the bsc_subsc or the subscr_conn, and then use it whenever we want to encode the MRPCI message.