e1000: Add PCI ID 0x10a4 for our new 4-port PCI-Express device

Device 0x10a4 is a double 82571 on a single PCI-Express card and
has 4 gigabit capable ports.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>