Add support for decoding Marvell (E)DSA tags

Add support for decoding Marvell (E)DSA tags

Similarly to commit 6eaebfe adding support for the Broadcom tagging
format supported by the DSA kernel subsystem, this commit adds support
for the Marvell DSA and Ethertype DSA (EDSA) tagging formats.

Marvell DSA is a 4-byte proprietary tag placed between the ether source
address and the ether length/type. It contains data such as the switch
device and port IDs from which a frame came from, or to which port
a frame is targetting. It also contains additional FPri and IEEE bits.

EDSA is a 8-byte variant including a programmable ethertype, two null
bytes and a standard DSA tag.