LU-8999 quota: fix issue of multiple call of seq start

LU-8999 quota: fix issue of multiple call of seq start

Multiple call of lprocfs_quota_seq_start could change the block
orders in the lower level of the quota tree, which will cause
quota entries to be skipped.

This patch also fix a problem in walk_tree_dqentry, which some
entries could be skipped for the "index" can be added even if
a valid quota entry has been found.

Change-Id: I44936c70d4060bd83db22aba0e3f665981cfa50a
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: https://review.whamcloud.com/31721
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>