sysmoBTS TCH: Set CMR in AMR RTP frames
sysmoBTS TCH: Set CMR in AMR RTP frames

Enable the previously commented-out logic to set the CMR (Codec Mode
Request) in AMR RTP frames based on the CMI (CMR Index) of the AMR
speech frame on the Um interface.

This is of course anyway the right thing to do, but also required for an
AMR receiver which doesn't have out-of-band information on the codec
mode, and which also doesn't determine the AMR codec mode based on the
size of the AMR frame (such as lcr as of current master).

We also move the entire CMR generation into the #ifdef section
which is only compiled-in if we do _not_ use the RTP mode of L1.

geosphere/osmo-bts,osmocom/osmo-bts,telenoobie/osmo-bts,telenoobie/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,telenoobie/osmo-bts,osmocom/osmo-bts,geosphere/osmo-bts,geosphere/osmo-bts,osmocom/osmo-bts