MAINTAINERS: Add headers and mailing list to UDP section

Add netdev mailing list and some more udp.h headers to the UDP section.
This is now more consistent with the TCP section.

Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241009-maint-net-hdrs-v2-2-f2c86e7309c8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: horms

MAINTAINERS

@@ -24184,8 +24184,12 @@ F:	drivers/usb/host/xhci*
 
 USER DATAGRAM PROTOCOL (UDP)
 M:	Willem de Bruijn <willemdebruijn.kernel@gmail.com>
+L:	netdev@vger.kernel.org
 S:	Maintained
 F:	include/linux/udp.h
+F:	include/net/udp.h
+F:	include/trace/events/udp.h
+F:	include/uapi/linux/udp.h
 F:	net/ipv4/udp.c
 F:	net/ipv6/udp.c