altos: Don't switch to flight 0 when log fills in flight

altos: Don't switch to flight 0 when log fills in flight

If the log is full at startup, we want to transmit flight 0 to let the
ground station know. However, we don't want to switch to flight 0 in
flight, so save the initial telemetry flight number (0 or the real
flight number) at startup and use that throughout the flight.

Signed-off-by: Keith Packard <keithp@keithp.com>