Changes

trau2rtp_hr16: change output format to RFC 5993

Emitting RFC 5993 payload format instead of TS 101 318 brings
Osmocom+E1 BSS into compliance with TS 48.103 (which requires
RFC 5993 format at AoIP interface), and will also make it much
easier to add optional support for TW-TS-002.

There are no backward compatibility issues: OsmoMGW E1 support
currently works only for FR and EFR, not for HR.

Related: OS#6448
Change-Id: I0bcfdccbf4df5a5cd90a65525527f08107be2cf5