Proper network topology, plus Steve's additions

The two SAS computers now have the proper internal network topology for flight.  Half of the magic is not in code, but rather in `iptables` rules on SAS1.

* SAS1 sends a duplicate of each command packet it receives to SAS2
* Only SAS1 will acknowledge the receipt of command packets (using telemetry type 0x01)
* Only SAS1 will start an additional thread that intercepts command packets from SAS2 bound for CTL and decides whether to send them along or discard them.
* Steve's additions for more getting commands (plus my fixes)

Merging immediately