coroutine: add flag to re-queue at front of CoQueue

coroutine: add flag to re-queue at front of CoQueue

When a coroutine wakes up it may determine that it must re-queue.
Normally coroutines are pushed onto the back of the CoQueue, but for
fairness it may be necessary to push it onto the front of the CoQueue.

Add a flag to specify that the coroutine should be pushed onto the front
of the CoQueue. A later patch will use this to ensure fairness in the
bounce buffer CoQueue used by the blkio BlockDriver.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20221013185908.1297568-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>