[exanic] Add PCI device ID for another X40 variant

Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/exanic.c

 	PCI_ROM ( 0x1ce4, 0x0004, "exanic-x10gm", "ExaNIC X10 GM", 0 ),
 	PCI_ROM ( 0x1ce4, 0x0005, "exanic-x40", "ExaNIC X40", 0 ),
 	PCI_ROM ( 0x1ce4, 0x0006, "exanic-x10hpt", "ExaNIC X10 HPT", 0 ),
+	PCI_ROM ( 0x1ce4, 0x0007, "exanic-x40g", "ExaNIC X40", 0 ),
 };
 
 /** ExaNIC PCI driver */