NFSv4: Avoid unnecessary scans of filesystems for returning delegations

NFSv4: Avoid unnecessary scans of filesystems for returning delegations

[ Upstream commit 35a566a24e58f1b5f89737edf60b77de58719ed0 ]

The amount of looping through the list of delegations is occasionally
leading to soft lockups. If the state manager was asked to return
delegations asynchronously, it should only scan those filesystems that
hold delegations that need to be returned.

Fixes: af3b61bf6131 ("NFSv4: Clean up nfs_client_return_marked_delegations()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>