s3:ctdbd_conn: simplify get_public_ips() / find_in_public_ips() API

s3:ctdbd_conn: simplify get_public_ips() / find_in_public_ips() API

These calls are used to check whether an IP address is static to the
host, or whether it could be migrated by ctdb.

Combine the calls into a simple ctdbd_public_ip_foreach(cb) function,
which avoids the need to expose struct ctdb_public_ip_list_old.

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Oct 14 12:29:56 UTC 2020 on sn-devel-184