ixgbe: Fixup the watchdog interrupt scheduling on 82599

The watchdog will schedule an interrupt to help make sure queues are
cleaned in the case when an interrupt is missed, most likely due to very
high load.  On 82599, there are extra interrupt registers to account for
the larger number of MSI-X vectors (64 total for 82599 vs. 18 total for
82598).  These must be taken into account when performing this operation in
the watchdog.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>