src: tproxy: relax family restrictions

src: tproxy: relax family restrictions

evaluation step currently prohibits

tproxy ip to 1.2.3.4 in ip family, and
tproxy ip6 to dead::1 in ip6.

This seems an arbitrary limitation, just accept this.
The current restriction would make json output support harder than needed,
as the tproxy expression generated from json path would have to
special-case the table its currently in, rather than just using the
family attribute in the json output.

We obviously still reject the family in case it mismatches
the table family (e.g., can't use ip address in ip6 table).

Signed-off-by: Florian Westphal <fw@strlen.de>