EX-8270 ptlrpc: rename 'pools' to 'ptr_pages'

EX-8270 ptlrpc: rename 'pools' to 'ptr_pages'

This finalizes the removal of the overloading of 'pools'
to also mean pointers of pages to items in each page pool.

This patch is currently the last in the series so it gets
full testing.  (This may change, but it's true now.)

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I0f4aba95f573f4afdc6f5d92f22fd67391fa6dab
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52461
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>