Feature: Add support for fake_rx_time

[bconway]

This is a useful feature in the Gateway Bridge for non-GPS gateways. It has a been mentioned on the forum as a roadblock to converting from Gateway Bridge, and I've experienced similar.

Thanks.

[mullerch]

I believe this belongs to the concentratord : chirpstack/chirpstack-concentratord#49

[bconway]

Negative, this feature request is for a setting comparable to what has existed in Gateway Bridge for a long time and works with the Semtech UDP forwarder. There are a number of gateways where I prefer not to use concentratord in favor of the buddled packet forwarder.

@brocaar has said he hopes to include this in the next release (or two).

[mullerch]

My bad you are right, I thought fake_rx_time was already in the Semtech UDP Packet Forwarder and this feature was for other backends.

[brocaar]

Hi @bconway and @mullerch the above commit implement the requested feature. I named it time_fallback_enabled as we are not really faking a time, we are providing a less accurate time in as a fallback.