net/sfc: support flow item VLAN in transfer rules

net/sfc: support flow item VLAN in transfer rules

Add support for this flow item to MAE-specific RTE flow implementation.

In a pattern, a L2 item preceding an item VLAN must have
correct "type" ("inner_type") set depending on the total
number of VLAN tags (double-tagging is supported):

"pattern eth type is X / vlan / end",
X = 0x8100, or 0x88a8, or 0x9100, or 0x9200, or 0x9300

"pattern eth type is X / vlan inner_type is 0x8100 / vlan / end"
X = 0x88a8, or 0x9100, or 0x9200, or 0x9300

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>