nft: swap key and direction in ct_dir syntax

nft: swap key and direction in ct_dir syntax

old: ct saddr original 1.2.3.4
new: ct original saddr 1.2.3.4

The advantage is that this allows to add ct keys where direction is optional
without creating ambiguities in the parser.

So we can have
ct packets gt 42
ct original packets gt 42

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