LU-10449 nrs: Generic TBF policy can't be shown correctly

LU-10449 nrs: Generic TBF policy can't be shown correctly

After setting TBF NID/OPCode/JobID policy and switch to generic
policy, the output of "lctl get_param ost.OSS.ost.nrs_policies"
can not display correctly.

Lustre-change: https://review.whamcloud.com/30696
Lustre-commit: 613f9cb553106316422db40e7f88baccf0438893

Change-Id: If8dcb7ae6ade634ec7ec4dfcb5887501cda90cdf
Signed-off-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Minh Diep <minh.diep@intel.com>
Reviewed-on: https://review.whamcloud.com/31397
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>