veth interfaces with untagged VLANs can't attach to bridges with no default PVID

[flisk]

Required information

• Distribution: Debian
• Distribution version: 12
• The output of
  • lxc-start --version 5.0.2
  • lxc-checkconfig (see below)
  • uname -a

Issue description

LXC containers will fail to start under the following conditions:

1. A veth network interface is configured in bridge mode and with an untagged VLAN ID
2. The configured bridge has no default PVID (vlan_default_pvid 0)

setup_veth_native_bridge_vlan will attempt to remove VLAN 0 from the veth interface, which fails because 0 is a special value indicating that interfaces added to the bridge receive no default PVID.

Example Startup Log

# lxc-start -F test1
lxc-start: test1: ../src/lxc/network.c: setup_veth_native_bridge_vlan: 471 Invalid argument - Failed to delete default untagged vlan "0" on "veth6yLhKO"
lxc-start: test1: ../src/lxc/network.c: netdev_configure_server_veth: 733 Invalid argument - Failed to setup native bridge vlan on "veth6yLhKO"
lxc-start: test1: ../src/lxc/network.c: lxc_create_network_priv: 3427 Invalid argument - Failed to create network device
lxc-start: test1: ../src/lxc/start.c: lxc_spawn: 1840 Failed to create the network
lxc-start: test1: ../src/lxc/start.c: __lxc_start: 2107 Failed to spawn container "test1"
lxc-start: test1: ../src/lxc/tools/lxc_start.c: main: 306 The container failed to start
lxc-start: test1: ../src/lxc/tools/lxc_start.c: main: 311 Additional information can be obtained by setting the --logfile and --logpriority options