MAINTAINERS: Cleanup Intel Wired LAN maintainers list

With the recent "retirements" and other changes, make the maintainers
list a lot less confusing and a bit more straight forward.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Shannon Nelson <sln@onemain.com>
Signed-off-by: David S. Miller <davem@davemloft.net>