nvme-fabrics: change NQN UUID to big-endian format

NVM Express 1.2.1 section 7.9, NVMe Qualified Names, specifies that the
UUID format of NQN uses a UUID based on RFC 4122.

RFC 4122 specifies that the UUID is encoded in big-endian byte order.

Switch the NVMe over Fabrics host ID field from little-endian UUID to
big-endian UUID to match the specification.

Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>