LU-17276 ldlm: convert flock locks to linux interval tree.

LU-17276 ldlm: convert flock locks to linux interval tree.

Convert to using the linux interval tree code.  When the range of a
lock is changed as part of adding or removing an overlapping range,
the lock is removed and readded to the tree.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I747b625af1e83210b12daac5102600a3de173a2a
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53950
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>