heartbeat-timeout < 30 seconds should not be allowed, or a serious warning should be shown

[hessu]

Someone just configured heartbeat-timeout 10, and then asked me why aprsc is rejecting the aprx.

Turned out that aprx was disconnecting due to the timeout every 10 seconds, since APRS-IS servers just don't send a heartbeat that often. The description of the timeout in the example config is maybe a bit difficult to understand.

IMHO it'd be nice if aprx would not allow a heartbeat-timeout value of less than 25 seconds at all, except when disabling the timeout (which would not be a great idea either, a serious warning should be logged).