Make libpcap parse following expressions, so tcpdump can filter 802.11 frames

Make libpcap parse following expressions, so tcpdump can filter 802.11 frames
based on frame types and/or subtypes:
tcpdump -ni wifi_iface -y ieee802_11 wlan type TYPE
tcpdump -ni wifi_iface -y ieee802_11 wlan type TYPE subtype SUBTYPE
tcpdump -ni wifi_iface -y ieee802_11 wlan subtype SUBTYPE

Thank Sam Leffer to point out that libpcap supports dynamic link layer headers.

# This commit has been merged into main stream code, so local patches can
# be nuked upon next vendor release updating.