Changes

bring twjit into libosmo-netif

twjit is the jitter buffer portion of Themyscira Wireless RTP
endpoint implementation, an alternative to Belledonne libortp.
Unlike Belledonne software, ThemWi RTP library was developed
specifically for use in Osmocom-based GSM, ISDN and IP-PSTN
network elements, and is built on top of libosmocore primitives -
thus it can function more natively in Osmocom universe than ortp.
This ThemWi library was initially developed externally to Osmocom,
but is now being brought into libosmo-netif so it can be used by
native Osmocom projects, particularly OsmoBTS.

Related: OS#6474
Change-Id: Ia3be5834571ca18b68939abbcf1ce3a879156658