sfc: save old MAC address in case sriov_mac_address_changed fails

Otherwise the PF and VF can disagree on the VF's MAC address and
this leads to strange behaviour, up to and including kernel panics.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/sfc/siena_sriov.h b/drivers/net/ethernet/sfc/siena_sriov.h
index 64e3e01..d88d4da 100644
--- a/drivers/net/ethernet/sfc/siena_sriov.h
+++ b/drivers/net/ethernet/sfc/siena_sriov.h
@@ -44,7 +44,7 @@
 int efx_siena_sriov_configure(struct efx_nic *efx, int num_vfs);
 int efx_siena_sriov_init(struct efx_nic *efx);
 void efx_siena_sriov_fini(struct efx_nic *efx);
-void efx_siena_sriov_mac_address_changed(struct efx_nic *efx);
+int efx_siena_sriov_mac_address_changed(struct efx_nic *efx);
 bool efx_siena_sriov_wanted(struct efx_nic *efx);
 void efx_siena_sriov_reset(struct efx_nic *efx);
 void efx_siena_sriov_flr(struct efx_nic *efx, unsigned flr);