nfp: add port state refresh

We will need a way of refreshing port state for link settings
get/set.  For get we need to refresh port speed and type.

When settings are changed the reconfiguration may require
reboot before it's effective.  Unregister netdevs affected
by reconfiguration from a workqueue.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>