network: refuse to create unsupported net types
network: refuse to create unsupported net types

Containers setup by unprivileged users are only able to create veth network
types.

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

aeris/lxc,terceiro/lxc,caglar10ur/lxc,caglar10ur/lxc,thmo/lxc,terceiro/lxc,LynxChaus/lxc,federicobriata/lxc,thmo/lxc,ss1h2a3tw/lxc,caglar10ur/lxc,aeris/lxc,federicobriata/lxc,hallyn/lxc,LynxChaus/lxc,ss1h2a3tw/lxc,terceiro/lxc,LynxChaus/lxc,hallyn/lxc,hallyn/lxc,federicobriata/lxc,aeris/lxc,ss1h2a3tw/lxc,thmo/lxc