MAINTAINERS: Intel nic drivers

Add a new F: line for the intel subdirectories.

This allows get_maintainers to avoid using git log
and cc'ing people that have submitted clean-up style
patches for all first level directories under
drivers/net/ethernet/intel/

This does not make e100.c maintained.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>