Changes

MGW control: migrate to new API for fmtp

Some codecs have additional parameters that need to be communicated
to the MGW using fmtp lines in SDP.  We use this mechanism to
indicate octet-align=0|1 for AMR and signal the use of TW-TS-001
and TW-TS-002 extensions for FR/EFR and HR, respectively.
Migrate from legacy struct mgcp_codec_param (now deprecated)
to the new fmtp string API.

Depends: I84ba2ed5ab9d379ac0b675520796446ad6ee0710 (osmo-mgw.git)
Change-Id: Id869c9fa33a3ca6fecd30d5630741fbbf21cf6ed