netfilter: nf_tables: add requirements for connsecmark support

Add ability to set the connection tracking secmark value.

Add ability to set the meta secmark value.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>