Restart WireGuard via cli

[yousong]

I assume ip link down

@trentmu

Alas, it does take the wg0 down
wgvpn0: ..... state DOWN mode DEFAULT group default qlen 1
but after the up (tried both command sets), it sets the state to
wgvpn0: ..... state UNKNOWN mode DEFAULT group default qlen 1
and the links don't re-establish.

That UNKNOWN is just expected.

I guess the difference is that when you do teardown/setup with netifd, the local listen port of wireguard interface change. From observers' point of view, it's new udp session. With ip link set down/up, the session is the same.