I reproduced this with the current lxd-3 in the tree as well. The reproduction steps are:

1. On a desktop Funtoo laptop with GNOME and NetworkManager running, and you're on a WiFi network...
2. Install lxd and configure it to set up a bridge (lxdbr0)
3. Start /etc/init.d/lxd (this triggers the bug)

What will then happen is that lxd will configure a default route for the bridge which will route all Internet traffic to the bridge. The NetworkManager icon will change from "WiFi" to "Ethernet connection" and network will not work, as lxdbr0 does not have a device on it with Internet access.

Bridge configuration:

config:
  ipv4.address: 10.132.238.1/24
  ipv4.nat: "true"
  ipv6.address: fd42:4c42:7c61:b77::1/64
  ipv6.nat: "true"
description: ""
name: lxdbr0
type: bridge
used_by:
- /1.0/instances/bugs-upgrade
managed: true
status: Created
locations:
- none 

Routing table:

valkyrie /home/drobbins # route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.132.238.1    0.0.0.0         UG    100    0        0 vethb2c28ed3
0.0.0.0         192.168.43.1    0.0.0.0         UG    600    0        0 wlan1
10.132.238.0    0.0.0.0         255.255.255.0   U     0      0        0 lxdbr0
10.132.238.0    0.0.0.0         255.255.255.0   U     100    0        0 vethb2c28ed3
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        0 lo
192.168.43.0    0.0.0.0         255.255.255.0   U     600    0        0 wlan1 

I am pointing to the first route in the list – which is a default route sending all traffic to the veth interface – as the problem. It overrides the second default route that already existed on the system (and is what I am using for WiFi). 

Workaround:

route del -net 0.0.0.0 gw 10.132.238.1 

I have not tested if this impacts container functionality.