When the tunnel is not in a position to work anymore, cancel the tunnel (i.e. tell the OS to dismantle the tunnel). Then the tunnel process shall exit and the on-demand shall make the OS launch the tunnel afresh when required. If we don't do this, the tunnel sometimes gets to a state where the tunnel process is alive but is not handing any packets.
Fixes #485.
When the tunnel is not in a position to work anymore, cancel the tunnel (i.e. tell the OS to dismantle the tunnel). Then the tunnel process shall exit and the on-demand shall make the OS launch the tunnel afresh when required. If we don't do this, the tunnel sometimes gets to a state where the tunnel process is alive but is not handing any packets.