l1sap: Drop unsupported HR GSM payload

Unfotunately there are two different RTP formats for HR GSM specified.
and it is unclear which should be used with GSM networks. Also each BTS
model may support only either one or the other format.

In the past this has lead to confusion and situations that were
difficult to debug. The reception of RTP packets in an unsupported
format may lead to unexpected behavior.

Let's introduce BTS_INTERNAL flags, one for each format and set them for
each BTS model accordingly. Then let's add a check to make sure
unsupported RTP payload is not forwarded to lower layers and appropriate
error messages are printed so that the problem does not go unnoticed.

Change-Id: I453562da412fde5b928bd2b588129c58ec8e2a7e
Related: OS#5688
---
M include/osmo-bts/bts.h
M src/common/bts.c
M src/common/l1sap.c
M src/osmo-bts-lc15/main.c
M src/osmo-bts-oc2g/main.c
M src/osmo-bts-sysmo/main.c
M src/osmo-bts-trx/main.c
M src/osmo-bts-virtual/main.c
8 files changed, 69 insertions(+), 0 deletions(-)