ixgbevf: fix MAC address changes through ixgbevf_set_mac()

Set hw->mac.perm_addr in ixgbevf_set_mac() in order to avoid losing the
custom MAC on reset. This can happen in the following case:

>ip link set $vf address $mac
>ethtool -r $vf

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>