sfc: add ndo_set_vf_link_state() function for EF10

Exercised with
"ip link set <PF intf> vf <vf_i> state {auto|enable|disable}"
Sets the reporting policy for VF link state to either
 - mirror physical link state
 - always up
 - always down

get VF link state mode in efx_ef10_sriov_get_vf_config

Exercised by
"ip link show <PF intf>";
output will include a line like
vf 0 MAC 12:34:56:78:9a:bc, link-state auto

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