CLEANUP: resolvers: properly initialize the sample in resolv_action_do_resolve()

CLEANUP: resolvers: properly initialize the sample in resolv_action_do_resolve()

The sample used to pass the IP address only had its data, px, sess and
strm fields initialized before being passed to vars_set_by_name(). It
turns out that this latter one doesn't seem to touch ctx, flags nor opt
but nothing guarantees it. Let's at least initialize the fields properly
to avoid passing random garbage.

No backport is needed.