tests: restrict ct saddr test to inet family

tests: restrict ct saddr test to inet family

any/ct.t: ERROR: line 94: src/nft add rule --debug=netlink ip6
test-ip6 output meta nfproto ipv4 ct original saddr 1.2.3.4: This rule should not have failed.

Actually, this failure is "ok; we can't find upper layer protocol
in this case, but even if we'd "fix" this it is still non-sensical,
meta nfproto ipv4, but family is ipv6 --> rule would never match.

First move this to an inet-specific test.
A followup patch will reject meta nfproto for all families except inet.

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