MAINTAINERS: Add self for the 3c509 network driver

MAINTAINERS: Add self for the 3c509 network driver

It appears there's a need for a maintainer for the 3Com EtherLink III
family of Ethernet network adapters.  There is documentation available
and the driver is very mature so the task ought to be of little hassle,
so I think I should be able to squeeze in any issues to be addressed.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/alpine.DEB.2.21.2604271056460.28583@angie.orcam.me.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>