igb: reset PHY after recovering from PHY power down

According to 82576_Datasheet.pdf, PHY setting is lost after PHY power down.
So resetting PHY is needed when recovering from PHY power down to set a default
setting to PHY register.
Owing to this lack, NIC doesn't link up in some rare situation.

Signed-off-by: Koki Sanagi <sanagi.koki@jp.fujitsu.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>