Configurable randomized value range for auto re-registration interval

[nanang]

Currently, auto re-registration (e.g: after transport disconnection) interval is configurable via reg_retry_interval/reg_first_retry_interval in the account config, and to avoid all clients re-registering at the same time, the interval will be randomized by +/- ten seconds. Note that the ten seconds random range is hardcoded. While for some cases, application may want the auto re-registration to be done immediately (no such randomized delay). Or even perhaps thinks that ten seconds random range is too tight/loose. This ticket will make the randomized range configurable.

Thanks Johan Lantz for the feedback.

[nanang]

In 4957:

Close #1802: Configurable randomized value range for auto re-registration interval.