Add (disabled) TDM_DEBUG to allow average_noise to debug tdm state times

[10:21:39 AM] Kevin Hester: hi tridge - I've noticed an interesting thing
about changing flight_time_estimate.  Applying an offset to the
calculated value only really seems to change the initial sync up of
two radios (the first time the receiver looks at trailer.window).
Because very quickly after initial connect they come to the same
agreement on what tdm_state_remaining should be.
[10:22:55 AM] Kevin Hester: (typical tdm_state_remaining is 6600
ticks ish so +/- 9 seems fine to me)