librbd/cache/pwl: fix endianness issue

librbd/cache/pwl: fix endianness issue

fix endianness issue with WriteLogCacheEntry encoding. abandon the
use of bits in the union. make '&' operation with the whole union
filed(flags) to get the bit information.

Fixes: https://tracker.ceph.com/issues/55389
Signed-off-by: Yin Congmin <congmin.yin@intel.com>
(cherry picked from commit 64f741ecebf3ff9a31d99f9f3d121ffeff54173b)

Conflicts:
	src/librbd/cache/pwl/Types.cc [ commit e96cdcb65851
	  ("librbd/cache/pwl: merge multiple output "<<" calls") not
	  in pacific ]