MAINTAINERS: step down as netfilter maintainer

I do not feel that I'm up to the task anymore.

I hope this to be a temporary emergeny measure, but for now I'm sure this
is the best course of action for me.
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240319121223.24474-1-fw@strlen.deSigned-off-by: Paolo Abeni <pabeni@redhat.com>

MAINTAINERS

@@ -15164,7 +15164,6 @@ F:	drivers/net/ethernet/neterion/
 NETFILTER
 M:	Pablo Neira Ayuso <pablo@netfilter.org>
 M:	Jozsef Kadlecsik <kadlec@netfilter.org>
-M:	Florian Westphal <fw@strlen.de>
 L:	netfilter-devel@vger.kernel.org
 L:	coreteam@netfilter.org
 S:	Maintained