net/sfc: implement transfer proxy port callback

net/sfc: implement transfer proxy port callback

In sfc, MAE admin serves as a transfer proxy. In order to track which
ethdev is privileged, augment every independent switch port structure
with information about its MAE privilege.

Signed-off-by: Viacheslav Galaktionov <viacheslav.galaktionov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>