LU-9385 mdt: remove XATTR locking from mdt_add_dirty_flag()

LU-9385 mdt: remove XATTR locking from mdt_add_dirty_flag()

Clients use the MDS_HSM_STATE_{GET,SET} RPCs to get and set the HSM
state of a file rather than accessing the HSM xattr directly. So
remove the use of MDS_INODELOCK_XATTR around the setting of HSM
attributes in mdt_add_dirty_flag().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I4374671ac5d4828480060de56c95ff7e1601fe59
Reviewed-on: https://review.whamcloud.com/26870
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>