Inconsistent query interval #79

Testing with Fresh Tomato 2021.2 K26ARM USB AIO-128K, which includes igmpproxy 0.3. Changelog: https://bitbucket.org/pedro311/freshtomato-arm/src/arm-master/CHANGELOG

I watched the packet capture for about 10 minutes and noticed that the interval between IGMPv2 Membership Query, general packets varied from about 6 seconds to 22 seconds. Generally, IGMP Queriers use a fixed interval between queries, with rfc2236 recommending a default of 125 seconds. A variable interval has the potential to cause issues on devices that base their "other querier present timer" (or equivalent monitoring function) on the detected interval between general queries.