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.