NETWORK BRIDGE

* In audiolinux lxqt you need first to disable or remove NetworkManager enable sytemd network and reboot (in a root terminal) :
systemctl disable NetworkManager
systemctl enable systemd-networkd
reboot
Also, you can use the pcmanfm-qt root file explorer (red icon on the bottom bar) instead of nano or mc for creating or editing files.
You should remove all occurrences of net.ifnames=0 from the configuration files /boot/syslinux/syslinux.cfg (for legacy boot) and /boot/EFI/boot/syslinux.cfg (for UEFI)

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If you need a Network Bridge it is advisable to use systemd network instead of NetworkManager, because "NetworkManager can create bridges, but currently will not auto-connect to them or slave/attached interfaces" cfr.: https://wiki.archlinux.org/index.php/Network_bridge

First we must remove net.ifnames=0 from all the configurations files inside /boot/loader/entries/
You can use mc (Midnight Commander) or nano
Example:
nano /boot/loader/entries/audiolinuxBFQ.conf
etc.
After you must reboot

Now let's go to /etc/systemd/network/
cd /etc/systemd/network/
We remove the previous files, if any
rm /etc/systemd/network/*

You can check the names of network interfaces with
ip addr show
In the examples that will follow we have 2 network interfaces, enp3s0 and enp4s0. Your names can be different.
--> In my test enp4s0 is connected to the router (and internet) and enp3s0 is connected directly from pc (with a normal ethernet cable) to a BeagleBone Black NAA running archlinuxarm 

This command will create the new files:
touch bridge0.netdev bridge0.network enp3s0.network enp4s0.network
Now you can edit the files with nano
nano /etc/systemd/network/bridge0.netdev
etc.
so that the content is:

1) bridge0.netdev

[NetDev]
Name=bridge0
Kind=bridge


2) bridge0.network (substitute values with yours)

[Match]
Name=bridge0

[Network]
DHCP=ipv4

Or enable both IPv4 and IPv6:

[Match]
Name=bridge0

[Network]

DHCP=yes

For static IPv4 address:

[Match]
Name=bridge0

[Network]
Address=192.168.1.5/24
Gateway=192.168.1.1

DNS=192.168.1.1

3) enp3s0.network

[Match]
Name=enp3s0

[Network]
Bridge=bridge0


4) enp4s0.network

[Match]
Name=enp4s0

[Network]
Bridge=bridge0


Finally we restart (or better reboot) systemd network:
systemctl restart systemd-networkd

Now, if you want to use this configuration with hqplayerd, this is an example of working configuration file (in /home/audiolinux/.hqplayer/hqplayerd.xml) where the relevant parameter related to the above configuration is:

<upnp interface="bridge0" />

hqplayerd.xml example

<?xml version="1.0" encoding="utf-8"?>
<xml>
    <title value="HQPlayer"/>
    <output type="network"/>
    <upnp interface="bridge0" />
  ...

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In case of problems follow these steps:

Test internet with:
ping 8.8.8.8

Check the content of /etc/resolv.conf with
cat /etc/resolv.conf
You should have
[audiolinux@archlinux ~]$ cat /etc/resolv.conf
nameserver 8.8.8.8


Also, check interfaces status with
networkctl
Example:
[audiolinux@archlinux ~]$ networkctl
IDX LINK             TYPE               OPERATIONAL SETUP   
  1 lo               loopback           carrier     unmanaged
  2 enp3s0           ether              degraded    configured
  3 enp4s0           ether              degraded    configured
  4 bridge0          bridge             routable    configured


Finally, we control the status of systemd network with
systemctl status systemd-networkd
Example:
[audiolinux@archlinux ~]$ systemctl status systemd-networkd
● systemd-networkd.service - Network Service
   Loaded: loaded (/usr/lib/systemd/system/systemd-networkd.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2018-09-21 09:32:08 CEST; 1h 52min ago
     Docs: man:systemd-networkd.service(8)
 Main PID: 478 (systemd-network)
   Status: "Processing requests..."
    Tasks: 1 (limit: 4915)
   Memory: 4.2M
   CGroup: /system.slice/systemd-networkd.service
           └─478 /usr/lib/systemd/systemd-networkd

You can also check errors in the linux journal with
journalctl -u network