[WireGuard] WireGuard doesn't work with network namespace on ArchLinux

[Jason A. Donenfeld]

Next time ask on the mailing list and not on stack overflow. Also
please use better subject lines in future emails. I'm going to paste
your stack overflow entry here, and then respond to that:

> Subject: Required key not available
> Content:
> i try to configure network with VPN (using WireGuard) and Network Namespace. Original instruction - www.wireguard.io/netns/
> I have a client (notebook) on ArchLinux and server (VPS) on ArchLinux. Client has IPv6-only network, server has dual-stack (IPv4 + IPv6) network.
> Client configs and output of some commands: http://pastebin.com/3Qy3PMrp
> Server: http://pastebin.com/CUizE4LS
> When netns.service started, i can ping fc00::10 (VPS, wg0 interface). But if i try ping any other resource (for example ping -6 -c 1 2a00:1450:4010:c01::8a (ipv6.google.com) ) i get an error:
> 'ping: sendmsg: Required key not available'
> Other commands (drill, tracepath6, traceroute, etc.) get the same error.
> I don't know how to fix it. Help please to solve this problem.
> $ cat /etc/wireguard/client.conf
> [Interface]
> PrivateKey = OAT5r6E1hid***iVBnY=
> ListenPort = 52345
> [Peer]
> PublicKey = aMC3f6kw***UDQVwo=
> EndPoint = [2a01:4f8:***:***::5]:40111
> AllowedIPs = fc00::10/7