This PR brings support of a shared port between stun (ICE agent) and
the kernel WireGuard
It implements a single port mode for execution with kernel WireGuard
interface using a raw socket listener.
BPF filters ensure that only STUN packets hit the NetBird userspace app
Removed a lot of the proxy logic and direct mode exchange.
Now we are doing an extra hole punch to the remote WireGuard
port for best-effort cases and support to old client's direct mode.
