Apply filtering with concentratord backend

[mullerch]

• [x] I have searched the issues of this repository and believe that this is not a duplicate.

Summary

The JoinEUI and NetID filters should be applied with the concentratord backend.

What is the use-case?

The same than the other backends ;-)

Implementation description

I don't think concentratord has filtering implemented. To me it makes sense taht the filtering is don in the gateway bridge as it's done by the semtech backend: https://github.com/chirpstack/chirpstack-gateway-bridge/blob/c83ee252c25452f193e9ed6868c035ec32d21207/internal/backend/semtechudp/backend.go#L509

Implementeation could be identical I guess : https://github.com/chirpstack/chirpstack-gateway-bridge/blob/c83ee252c25452f193e9ed6868c035ec32d21207/internal/backend/concentratord/concentratord.go#L319

Can you implement this by yourself and make a pull request?

If necessary