e1000e: Fix irq_synchronize in MSI-X case

Based on original patch/work from Jean Delvare <jdelvare@suse.de>
Synchronize all IRQs when in MSI-X IRQ mode.

Jean's original patch hard coded the sync with the 3 possible vectors,
this patch incorporates more flexibility for the future and aligns
with how igb stores the number of vectors into the adapter structure.

CC: Jean Delvare <jdelvare@suse.de>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Acked-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>