virtio-blk: tolerate failure to set BlockBackend AioContext

virtio-blk: tolerate failure to set BlockBackend AioContext

We no longer rely on setting the AioContext since the block layer
IO_CODE APIs can be called from any thread. Now it's just a hint to help
block jobs and other operations co-locate themselves in a thread with
the guest I/O requests. Keep going if setting the AioContext fails.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240119135748.270944-6-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>