Fix validation of overly-long IPv6 addresses.
Fix validation of overly-long IPv6 addresses.

The inet/cidr types sometimes failed to reject IPv6 inputs with too many
colon-separated fields, instead translating them to '::/0'.  This is the
result of a thinko in the original ISC code that seems to be as yet
unreported elsewhere.  Per bug #14198 from Stefan Kaltenbrunner.

Report: <0156d2bcd061973387a54b65a763bd2eeb38b62a@wrigleys.postgresql.org>

ashwinstar/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,lisakowen/gpdb,jmcatamney/gpdb,adam8157/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb