sfc: MC_CMD_SET_MAC can only be called by the link control Function

MC_CMD_SET_MAC is privileged and can only by called by the link
control function.

This patch adds efx_ef10_mac_reconfigure_vf which avoids the call
to MC_CMD_SET_MAC by the Virtual function

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