MAINTAINERS: add Paul Fertser as a NC-SI reviewer

Paul has been providing very solid reviews for NC-SI changes
lately, so much so I started CCing him on all NC-SI patches.
Make the designation official.

Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Link: https://patch.msgid.link/20250123155540.943243-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>