LU-11085 llite: reimplement range_lock with Linux interval_tree

LU-11085 llite: reimplement range_lock with Linux interval_tree

As a step towards removing the lustre interval-tree implementation,
reimplent range_lock to use Linux interval trees.

As Linux interval trees allow the same interval to be stored twice,
this allows the removal of the rl_next_lock list and associated code.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I1d1669345fac0945e0e189b87a74ca8e7582e842
Reviewed-on: https://review.whamcloud.com/39726
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>