[feature request] filter out advertisement duplicates

[bam80]

In a passive scanning mode, the data usually duplicated several times between the neighbor advertisements.
This is inevitable measure for BLE 4.x to counter overlaps, etc.
pvvx/ATC_MiThermometer#450 (comment)

From informational point of view, such duplicated packets do not hold a new data (those might still be useful for the statistics, though).
It would be good to have ability to filter them out, and only send out MQTT packets for a new data in the advertisements.

In both alternative firmware's (and maybe others), Bluetooth Advertising Format has "measurement counter" field increased with each new measurement.
We could optionally send out a new MQTT packets only when the counter increases, thus filtering the duplicates out.

I tried to make the advertisement interval wider, but that's restricted by BLE 4.x standards to 10 sec max.

The MQTT app I use has limited amount of stored packets for graph's history data, thus the filtering feature of the MQTT gateway is essential there.