netfs: Fix wait/wake to be consistent about the waitqueue used

netfs: Fix wait/wake to be consistent about the waitqueue used

Fix further inconsistencies in the use of waitqueues
(clear_and_wake_up_bit() vs private waitqueue).

Move some of this stuff from the read and write sides into common code so
that it can be done in fewer places.

To make this work, async I/O needs to set NETFS_RREQ_OFFLOAD_COLLECTION to
indicate that a workqueue will do the collecting and places that call the
wait function need to deal with it returning the amount transferred.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/20250519090707.2848510-5-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Steve French <stfrench@microsoft.com>
cc: Ihor Solodrai <ihor.solodrai@pm.me>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: v9fs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>