US915 Uplink/Downlink channel missmatch

[Malum2600]

I'm not sure if this issue should be addressed in the Concentratord or the Mesh programing but the issue impacts the Mesh operations in the US915 frequencies. In EU868 the uplink and downlink frequencies are the same so the error does not occur, but in US915 that is not the case.
In Mesh when the relay gateway is sending a mesh frame using US915 to the boarder gateway it is assigning a downlink_id but using an uplink frequency.

chirpstack-gateway-mesh[2221]: Sending mesh frame - [downlink_id: 376928261 - [freq: 902900000, power: 21, mod: [LORA - sf: 10, bw: 125000], timing: [IMMEDIATELY]]]
chirpstack-concentratord-sx1302[1676]: Frequency is not within min/max gateway frequency, downlink_id: 376928261, min_freq: 923000000, max_freq: 928000000

I see 3 ways to fix this but not sure which is the most correct.

1. This downlink should really be an uplink since the relay gateway is the endpoint sending a hearbeat packet up to the network server.
2. Change the frequencies Mesh is using to communicate frames so it uses US915 downlink frequencies.
3. Change Conectratord so the US915 radio_min_max_tx_freq is 902 to 928, but I believe that violates the LoRa standard since it would then be transmitting downlinks on the uplink channels.

Discussion of the issue on the Chirpstack forums.
https://forum.chirpstack.io/t/gateway-mesh-us915-setup-issues/22062

[brocaar]

This is already fixed in the Concentratord