dns_portlist_create(), dns_portlist_add(),
dns_portlist_remove(), dns_portlist_match(),
dns_portlist_attach() and dns_portlist_detach().
1441. [func] It is now possible to tell dig to bind to a specific
source port.
1440. [func] It is now possible to tell named to avoid using
certian source ports (avoid-v4-udp-ports,
avoid-v6-udp-ports).
developer: marka
reviewer: explorer