Serial port activity?

[admin]

So, it looks like there is a 2nd activity related S-register, S73. This is a "no activity" timeout that will ping the other modem (real phone modem) to see if it is there. We already do that through the router portal. So, I think it would be safe to re-purpose this as a hard cutoff of the connection based on time, using the same parameters that we use for S30. I will look into how much work this is because I am not sure how much of a pain it is for non-consecutive S-register values to be handled in the code.