SDP/MGCP: pass octet-align=1 for AMR / pass all fmtp

Since recent libosmo-mgcp-client update (see Depends), we can now pass
fmtp for each individual codec entry to be sent in the SDP. Use that new
feature to pass any fmtp from rtp_stream.c to the MGW via MGCP.

In effect, this adds the 'octet-align=1', defined in codec_mapping.c as
the default for AMR, which was missing from the SDP/MGCP that osmo-msc
sends out.

A 2G to 2G call worked out OK without it, because omitting the
'octet-align' setting from MGCP disables all octet-align payload checks
in osmo-mgw. Both 2G call legs use octet-align=1, and things work out.

Running a call from 3G to 2G before this patch would result in osmo-mgw
dropping the RTP with logging like:

  DRTP NOTICE (rtpbridge/1@bsc0 I:B38CF524) rx_rtp(44 bytes): Expected RTP AMR octet-aligned=1 but got octet-aligned=0. check the config of your call-agent! (mgcp_network.c:1527)

...because osmo-bsc's MGW was instructed to expect octet-align=1, while
osmo-msc's MGW emits octet-align=0. This happens because converting the
3G IuUP to 2G AMR heeds the RFC 6871 specified default of octet-align=0.

So, after this patch, we accurately send "octet-align=1", and make the
IuUP-to-AMR conversion emit octet-align=1 to match 2G.

Side note: 3GPP specifies AoIP to use bandwidth-efficient AMR only;
however, in all known Osmocom world, our 2G BTS emit octet-aligned AMR
instead -- so in practice it makes most sense to run osmo-msc with
octet-align=1 as the default. osmo-msc shall at some point feature a
.cfg option to switch to octet-align=0 to conform with 3GPP, but until
then, osmo-msc now configures all AMR to be octet-align=1.

Depends: osmo-mgw If58590bda8627519ff07e0b6f43aa47a274f052b
Change-Id: Ief9225c9bcf7525a9a0a07c282ffb8cc0d092186
---
M TODO-RELEASE
M configure.ac
M src/libmsc/rtp_stream.c
3 files changed, 44 insertions(+), 1 deletion(-)