0.9.28: better enforcement of DHT upload rate limit for non-locally generated requests.
the limit applies to: DHT replies, refreshes of stored items, checking for status/tracker and proxy server.
local requests (eg. dhtgets from the UI) are excluded from this limit, so user experience is not affected.
in other words: we limit only the band contributed back to twister network for maintenance tasks.

this should improve resilience against some sorts of denial-of-service attacks and also
prevents saturating the uplink as observed recently.