sfxge(4): support VNI/VSID and inner frame local MAC

This supports VNI/VSID and inner frame local MAC fields to
match in VXLAN, GENEVE, or NVGRE packets.

Submitted by: Roman Zhukov <roman.zhukov at oktetlabs.ru>
Sponsored by: Solarflare Communications, Inc.
Differential Revision: https://reviews.freebsd.org/D18218