sfc: record the PF's vport ID in nic_data

The default port ID of EVB_PORT_ID_ASSIGNED is a "magic" number
for the MCFW to select the physical port of the PF.  If other
vswitches and vports are created on top of the default firmware
configuration, the ID of the newly created vport is then required
when passed to MCDI commands.  Currently, this doesn't happen so
the vport_id is never changed, but a subsequent patch will change
this behaviour so that other vswitches and vports are created.

The vport_id recorded in nic_data is only relevant for PFs.
VFs will have their vports created by their parent PF, and in
that case the parent PF will record the vport ID of each VF.
For a VF, nic_data->vport_id is expected to remain at the default
value.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>