MAINTAINERS: update netfilter maintainers

Marc Boucher, James Morris and Rusty Russell were crucial in the
early netfilter days. We thank them all!

However, they are not actively maintaining netfilter anymore.

This patch adds myself as netfilter maintainer.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

MAINTAINERS

@@ -4452,11 +4452,9 @@ F:	Documentation/networking/vxge.txt
 F:	drivers/net/ethernet/neterion/
 
 NETFILTER/IPTABLES/IPCHAINS
-P:	Rusty Russell
-P:	Marc Boucher
-P:	James Morris
 P:	Harald Welte
 P:	Jozsef Kadlecsik
+M:	Pablo Neira Ayuso <pablo@netfilter.org>
 M:	Patrick McHardy <kaber@trash.net>
 L:	netfilter-devel@vger.kernel.org
 L:	netfilter@vger.kernel.org