LU-17383 statahead: quit statahead with a long time wait

LU-17383 statahead: quit statahead with a long time wait

If the thread is not doing stat for more than a time threshold
(@sbi->ll_sa_timeout, 30 seconds by default) then it probably does
not care too much about performance, or is no longer using this
directory.
Quit the statahead thread with a long time wait in this case.

This patch also fixes defects reported by Coverity Scan for
Lustre.

Also add the lines about ll_sa_timeout in
https://review.whamcloud.com/41308

Lustre-change: https://review.whamcloud.com/53535
Lustre-commit: cfcba1ede861faec33d797e876a0fb11eab4332a

Fixes: e10bf68d7c3 ("LU-14361 statahead: regularized fname statahead pattern")
Test-Parameters: testlist=parallel-scale-nfsv4
Test-Parameters: testlist=parallel-scale-nfsv4
Test-Parameters: testlist=parallel-scale-nfsv4
Test-Parameters: testlist=parallel-scale-nfsv4
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Ia7c478268fe12eeefa6dfae1b3c94451f010d1d5
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/55014
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>