MAINTAINERS: add entry for libeth and libie

Add myself as a maintainer/supporter for libeth and libie. Let they have
separate entries from the Intel ethernet code as it's a bit different
case and all patches will go through me rather than Tony.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>