MAINTAINERS: add second list for IRDA

The irda-users-list is currently almost dead and subscribers-only. Adding
netdev increases the audience which might help to not overlook a bugreport
again.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>