igbvf: Regard vf reset nack as success

vf reset nack actually represents the reset operation itself is
performed but no address is assigned. Therefore, e1000_reset_hw_vf
should fill the "perm_addr" with the zero address and return success on
such an occasion. This prevents its callers in netdev.c from saying PF
still resetting, and instead allows them to correctly report that no
address is assigned.

Fixes: 6ddbc4cf ("igb: Indicate failure on vf reset for empty mac address")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Tested-by: Marek Szlosek <marek.szlosek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>