...after ~70sec of no activity

I (39527861) wifi: state: run -> auth (7c0)
I (39527861) wifi: n:11 0, o:11 0, ap:255 255, sta:11 0, prof:1
I (39527862) wifi: pm stop, total sleep time: 0/848270267

32mI (39527865) wifi: SYSTEM_EVENT_STA_DISCONNECTED

this might have been fixed in sdk already ('sending null frame'...) but in 2.1 causes problems - w/o a buffer for results, data is being lost. also, ssl often fails just after reconnecting.
we can send a simple request every 30 sec or so, maybe even only to the gateway.