LU-16430 ptlrpc: racy rq_obsolete bit modification

LU-16430 ptlrpc: racy rq_obsolete bit modification

Racy bit modification causes assertion failure in
ptlrpc_at_remove_timed():
ASSERTION( !list_empty(&req->rq_srv.sr_timed_list) )

rq_obsolete is a bit field, so it's modification
isn't atomic and should be modified under rq_lock.

Lustre-Commit: 14ac768fd9633c5cf4474555170e5042c71a135b
Lustre-Change:  https://review.whamcloud.com/49505

Change-Id: Ib1d3ad189a78b71ecf5b01585478922e984c9568
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/55086
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>