LU-14741 obdclass: Wake up queue of reqs on close completion

LU-14741 obdclass: Wake up queue of reqs on close completion

Origin title:
LU-14741 obdclass: Wake up entire queue of requests on close
completion

Since close requests could be stuck behind normal requests and get
more slots we need to wake up entire accumulated queue waiting
for the next modrpc slot or have additional waitqueue just for
close requests.

This patch goes with the former approach.

Lustre-change: https://review.whamcloud.com/43941
Lustre-commit: a4e1567d67559b797a5c24ee0bfbca4a52649c47

Fixes: 1fc013f901 ("LU-5319 mdc: manage number of modify RPCs in flight")
Change-Id: Ib4333c7f6731dd435364d5e5f529577a1600a235
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-on: https://review.whamcloud.com/44288
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>