ChirpStack Gateway Bridge binds to udp6 only

[soosp]

• [x] The issue is present in the latest release.
• [x] I have searched the issues of this repository and believe that this is not a duplicate.

What happened?

If you have IPv6 configured and set

udp_bind = "0.0.0.0:1700"

in your /etc/chirpstack-gateway-bridge/chirpstack-gateway-bridge.toml file (this isthe default setting), ChirpStack Gateway Bridge binds to ipv6 socket only:

# netstat -lnup | grep 1700
udp6       0      0 :::1700                 :::*                                4077/chirpstack-gat

If you set a valid IPv4 socket, it binds only to it as expected.

Tested with the latest precompiled Debian binaries.

What did you expect?

It binds only IPv4 socket or both IPv4 and IPv6.

Steps to reproduce this issue

Steps:

1. Set up an IPv4 end IPv6 dual stack configuration with static adresses.
2. Leave udp_bind parameter on the default 0.0.0.0:1700 value.
3. See if it binds to the IPv4 socket.

Could you share your log output?

# chirpstack-gateway-bridge -c /etc/chirpstack-gateway-bridge/chirpstack-gateway-bridge.toml
INFO[0000] starting ChirpStack Gateway Bridge            docs="https://www.chirpstack.io/gateway-bridge/" version=4.0.11
INFO[0000] backend/semtechudp: starting gateway udp listener  addr="0.0.0.0:1700"
WARN[0000] [store]    memorystore wiped                  module=mqtt
INFO[0000] integration/mqtt: connected to mqtt broker

Your Environment

Component	Version
Application Server
Network Server
Gateway Bridge	v4.0.11
Chirpstack API
Geolocation
Concentratord