The socket is wanted by sockets.target and nothing orders the wireguard
unit before it, so the mesh address can be missing at bind time
(EADDRNOTAVAIL) and the receiver never listens. FreeBind lets the bind
succeed regardless, and also covers the interface coming back after a flap.
Also assert the mesh address is not a wildcard, which the comment above the
socket already claimed, and cover the rendered socket in a module-eval case.
