LU-17431 nodemap: introduce helper funcs for range handling

LU-17431 nodemap: introduce helper funcs for range handling

Introduce helper functions for NID range handling on nodemaps,
to make it possible to use recursively for NID4 ranges:
__range_insert
__range_find
__range_search
__range_delete

Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I1ec0dff1c38111621678a0e79e00c7789bcc5b8b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54735
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>