Quick bug-fix release to further improve our Fruity backend, where @hsorbo and I filled up our coffee cups and hammered out the following fixes:

• tunnel-connection: Wire up missing stream close logic.
• tunnel-connection: Ensure JSON request ends up in its own UDP packet. When opening the tunnel, it seems problematic if a datagram and stream data end up in the same UDP packet. We make our dummy-datagram larger to avoid this.
• tunnel-connection: Consistently avoid writes after connection is gone, which would result in a crash.
• network-stack: Handle perform_on_lwip_thread() from the lwIP thread instead of deadlocking.