portmap check fails looking for non-existent IPv6 rule

[mccv1r0]

cniAdd portmap with only an IPv4 address configured for an interface. Only ipv4 nat rules are created.

cniCheck fails expecting to find ip6tables nat rules. cniDel has similar logic, but is more forgiving when a rule doesn't exist

maybeGetIptables() always returns a struct, even when there are no rules for this container. This results in the test on ip6t always trying to check/del ipv6

	ip6t, err6 := maybeGetIptables(true)
        [deleted]
	if ip6t != nil {
	}