libxtables: avoid confusing use of ai_protocol=IPPROTO_IPV6

[Split hunk from Wes's submission. Added commit message. -j.eng]

ai_protocol normally specifies the L4 protocol one wants to
specifically inquire about when a service (2nd parameter to
getaddrinfo) is specified. Such a service lookup would potentially
yield nothing, because there just is not any "mytunnel 2222/ipv6" in
/etc/services, since IPPROTO_IPV6 itself is not a protocol with a
concept of (port-based) services to begin with.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
1 file changed