client: using hash value to compose dentry offset

client: using hash value to compose dentry offset

If MDS sorts dentries in dirfrag in hash order, we use hash value to
compose dentry offset. dentry offset is:

  (0xff << 52) | ((24 bits hash) << 28) |
  (the nth entry hash hash collision)

This offset is stable across directory fragmentation.

Signed-off-by: Yan, Zheng <zyan@redhat.com>
(cherry picked from commit 680766ec131b95271e320f54dfe6d69ea8d4fbb3)

Signed-off-by: Greg Farnum <gfarnum@redhat.com