Add 3GPP2 Tx AVPs.  Move all the 3GPP2 stuff into its own XML file.

Change-Id: I7197f84472139c99bafa5b68f724abaab0453faa
Reviewed-on: https://code.wireshark.org/review/3908
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>