LinuxKPI: if_ether additions

Add various protocol IDs found in various wireless drivers.
Also add ETH_FRAME_LEN and struct ethhdr.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D29397

(cherry picked from commit 3cce818c46f58c0089d34a00478c3b7fa3b57c09)