wpa: Enable receiving priority tagged (VID 0) frames

Certain internet service providers transmit vlan 0 priority tagged
EAPOL frames from the ONT towards the residential gateway. VID 0
should be ignored, and the frame processed according to the priority
set in the 802.1P bits and the encapsulated EtherType (i.e. EAPOL).

The pcap filter utilized by l2_packet is inadquate for this use case.

Here we modify the pcap filter to accept both unencapsulated and
encapsulated (with VLAN 0) EAPOL EtherTypes. This preserves the
original filter behavior while also matching on encapsulated EAPOL.

Sponsored by: Rubicon Communications, LLC ("Netgate")
Reviewed by: cy
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D40442