net/sfc/base: export the zero-based MCDI port number

net/sfc/base: export the zero-based MCDI port number

Proxy authorization module for SR-IOV requires one instance of proxy
data structures per card. In order to achieve this, proxy data
structures will be allocated only for primary port (port id 0) and other
secondary ports in the card will access those data structures through
reference to primary port. Accordingly, the port number obtained from
efx_mcdi_get_port_assignment is stored in NIC configuration as
enc_mcdi_port.

Signed-off-by: Gautam Dawar <gdawar@solarflare.com>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>