cifs: ensure we revalidate the inode after readdir if cifsacl is enabled

Otherwise, "ls -l" will simply show the ownership of the files as
the default mnt_uid/gid. This may make "ls -l" performance on large
directories super-suck in some cases, but that's the cost of cifsacl.

One possibility to make it suck less would be to somehow proactively
dispatch the ACL requests asynchronously from readdir codepath, but
that's non-trivial to implement.

Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>