If we get a ESTALE on readdir retry the dirent
as we might have hit with a old dirent which we kept for
performance reasons

Signed-off-by: Venkateswararao Jujjuri "<jvrao@linux.vnet.ibm.com>
Signed-off-by: Rong Zeng <rongzeng@us.ibm.com>
cache_inode_add_cached_dirent should return reused dirent
inaddition to just copying it.

Signed-off-by: Venkateswararao Jujjuri "<jvrao@linux.vnet.ibm.com>