LU-9227 nrs: Rate change of a TBF rule loses control

LU-9227 nrs: Rate change of a TBF rule loses control

In some test cases, i.e.
	start dd_0 {dd.0} 1000
	dd if=/dev/zero of=/mnt/lustre/test bs=1M count=100
	start dd_1000 {dd.1000} 1000
After ran above commands, changing rate of dd_0 take no effect.
The reason is that starting rule dd_1000 increases the sequence,
but the sequence number of the class with id "dd.0" does not
change accordingly, resulting in failure of rate change.
This patch fixes this problem.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I9cdd469fd57dea692b86285cc26040a117b120ad
Reviewed-on: https://review.whamcloud.com/26085
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>