rgw: Fixed several bugs in policies related to IPv6 addresses.

rgw: Fixed several bugs in policies related to IPv6 addresses.

The IPv6 conversion was not properly converting the address to host byte
order.
The text conversion of IPv6 addresses was using raw byte values instead of
the converted number. The portions of the addresses were grouped by bytes
instead of 16-bit words. The prefix length was erroneously being rendered
in hex.

http://tracker.ceph.com/issues/20991

Signed-off-by: John Gibson <jgibson@mitre.org>
(cherry picked from commit a25ca37401d1e8dc4349201b9f64aa6990bea0d5)