LinuxKPI: if_ether additions

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

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