lcls: set codec info when performing MGW operation

While GSCON is setting the codec info when operating on the MGW, LCLS
is not doing that yet. This means that the MDCX messages that are
sent by LCLS do not contain any payload type and also no ptime or
rtpmap fields. This also causes the following TTCN3 tests to fail:

TC_lcls_connect_break
TC_lcls_connect_clear
TC_lcls_gcr_bway_connect
TC_lcls_gcr_bway_dont_connect_csc

- Make mgcp_pick_codec() public as bsc_subscr_pick_codec()
- use bsc_subscr_pick_codec() to set codec info in osmo_bsc_lcls.c

Change-Id: I383d55fa602cda0926dd701ee517a299db578260
Closes: OS#3358
3 files changed