LU-16160 osc: take ldlm lock when queue sync pages

LU-16160 osc: take ldlm lock when queue sync pages

osc_queue_sync_pages() add osc_extent to osc_object's IO extent
list without taking ldlm locks, and then it calls
osc_io_unplug_async() to queue the IO work for the client.

This patch make sync page queuing take ldlm lock in the
osc_extent.

Lustre-change: https://review.whamcloud.com/48557
Lustre-commit: 67aca1fcc6bed20794832decdba590a758d67d8fp

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Idefa2981e62a2a6e10d8b8a7692c0337b61b9052
Reviewed-on: https://review.whamcloud.com/48597
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>