ceph: voluntarily drop Fx cap for readdir request

MDS need to rdlock directory inode's filelock when handling readdir
request. Voluntarily dropping CEPH_CAP_AUTH_EXCL avoids a cap revoke
message.
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/dir.c

@@ -381,6 +381,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
 		if (op == CEPH_MDS_OP_READDIR) {
 			req->r_direct_hash = ceph_frag_value(frag);
 			__set_bit(CEPH_MDS_R_DIRECT_IS_HASH, &req->r_req_flags);
+			req->r_inode_drop = CEPH_CAP_FILE_EXCL;
 		}
 		if (fi->last_name) {
 			req->r_path2 = kstrdup(fi->last_name, GFP_KERNEL);