migration: poll the cm event while wait RDMA work request completion

migration: poll the cm event while wait RDMA work request completion

If the peer qemu is crashed, the qemu_rdma_wait_comp_channel function
maybe loop forever. so we should also poll the cm event fd, and when
receive RDMA_CM_EVENT_DISCONNECTED and RDMA_CM_EVENT_DEVICE_REMOVAL,
we consider some error happened.

Signed-off-by: Lidong Chen <[email protected]>
Signed-off-by: Gal Shachaf <[email protected]>
Signed-off-by: Aviad Yehezkel <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Signed-off-by: Juan Quintela <[email protected]>