Add initial 3GPP LCLS support to OsmoBSC

This code contains the following code:
* receive/parse/interpret LCLS specific BSSMAP IEs and PDUs
* osmo_fsm handling the various states and their transitions
* call leg correlation (finding the other subscr_conn with same GCR)
* communication between the two call-leg LCLS FSMs
* detection of supported / unsupported LCLS configurations
* display of GCR / LCLS information in "show conns"
* switch the media streams locally using MDCX to the MGW

Closes: OS#1602
Change-Id: I614fade62834def5cafc94c4d2578cd747a3f9f7
11 files changed