LU-17249 ptlrpc: protect scp_rqbd_idle list operations

LU-17249 ptlrpc: protect scp_rqbd_idle list operations

Protect scp_rqbd_idle list entry getting by spinlock
in ptlrpc_service_purge_all() like it does in all
other places where rqbd_list linkage is being managed

Lustre-change: https://review.whamcloud.com/52931
Lustre-commit: 9ba375983d498690f5caa29c289c137470a76505

Test-Parameters: testgroup=full-part-1 env="SLOW=yes,ENABLE_QUOTA=yes"
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: Iace37b1ee79bfd0c3a54a35722952e17d860a91c
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52952
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>