LU-9859 ptlrpc: simplify nrs_tbf_jobid_list_parse()

LU-9859 ptlrpc: simplify nrs_tbf_jobid_list_parse()

If we duplicate the string passed to nrs_tbf_jobid_list_parse(), we
can parse using standard mutating tools.

Test-Parameters: trivial
Test-Parameters: testlist=sanityn env=ONLY=77
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Id04390c2ed0a26a0311a8bbc784979eb18f4d19d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50838
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>