No NICs need to switch efx_mac_operations at run-time, and the MAC
operations are fairly closely bound to NIC types.

Move efx_mac_operations::reconfigure to efx_nic_type::reconfigure_mac
and efx_mac_operations::check_fault fo efx_nic_type::check_mac_fault.
Change callers to call through efx->type or directly if the NIC type
is known.

Remove efx_mac_operations::update_stats.  The implementations for
Falcon used to fetch MAC statistics synchronously and this was used by
efx_register_netdev() to clear statistics after running self-tests.
However, it now only converts statistics that have already been
fetched (and that only for Falcon), and the call from
efx_register_netdev() has no effect.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>