migration/rdma: Send error during cancelling

migration/rdma: Send error during cancelling

When we issue a cancel and clean up the RDMA channel
send a CONTROL_ERROR to get the destination to quit.

The rdma_cleanup code waits for the event to come back
from the rdma_disconnect; but that wont happen until the
destination quits and there's currently nothing to force
it.

Note this makes the case of a cancel work while the destination
is alive, and it already works if the destination is
truly dead.  Note it doesn't fix the case where the destination
is hung (we get stuck waiting for the rdma_disconnect event).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20170717110936.23314-7-dgilbert@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>