The POSIX says we should return -ENODATA when the corresponding
attribute doesn't exist when removing it. While there is one
exception for the acl ones in the local filesystems, for exmaple
for xfs, which will treat it as success.

While in the MDS side there have two ways to remove the xattr:
sending a CEPH_MDS_OP_SETXATTR request by setting the 'flags' with
CEPH_XATTR_REMOVE and just issued a CEPH_MDS_OP_RMXATTR request
directly.

For the first one it will always return 0 when the corresponding
xattr doesn't exist, while for the later one it will return
-ENODATA instead, this should be fixed in MDS to make them to be
consistent.

Added a CEPH_XATTR_REMOVE2 new flags and will return -ENODATA errno
directly when the crresponding xattr doesn't exist. Just keeps the
old CEPH_XATTR_REMOVE flags to make it to be compatible with old
clients.

Fixes: https://tracker.ceph.com/issues/64679
Signed-off-by: Xiubo Li <xiubli@redhat.com>
(cherry picked from commit 797e926)