ixgbe: fix for race with 8259(8|9) during shutdown

There is a small window where the watchdog could be running as the
interface is brought down on a NIC with two ports wired back to back.
If ixgbe_update_status is then called can lead to a panic.  This patch
allows the update to bail if we are in that condition.

This issue was orignally reported and fix proposed by Akihiko Saitou.

CC: Akihiko Saitou <asaitou@users.sourceforge.net>
Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>