packet-raknet.c: value_string array (created at runtime) must be terminated with {0, NULL}.

This should fix crash in 'tshark -G values' seen on 64 bit tshark.

Change-Id: Ia183fc5d5604f71b824cf4f758c18ff1ccd4540f
Reviewed-on: https://code.wireshark.org/review/4694
Reviewed-by: Bill Meier <wmeier@newsguy.com>