MAINTAINERS: Add linux.nics@intel.com to INTEL ETHERNET DRIVERS

If this is added to the driver files, then maybe it's
appropriate to add to MAINTAINERS as well.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>