wgengine/wgcfg: recover from mismatched PublicKey/Endpoints

In rare circumstances (tailscale/corp#3016), the PublicKey
and Endpoints can diverge.

This by itself doesn't cause any harm, but our early exit
in response did, because it prevented us from recovering from it.

Remove the early exit.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

wgengine/wgcfg/config.go

@@ -28,6 +28,11 @@ type Peer struct {
 	DiscoKey            key.DiscoPublic // present only so we can handle restarts within wgengine, not passed to WireGuard
 	AllowedIPs          []netaddr.IPPrefix
 	PersistentKeepalive uint16
+	// wireguard-go's endpoint for this peer. It should always equal Peer.PublicKey.
+	// We represent it explicitly so that we can detect if they diverge and recover.
+	// There is no need to set WGEndpoint explicitly when constructing a Peer by hand.
+	// It is only populated when reading Peers from wireguard-go.
+	WGEndpoint key.NodePublic
 }
 
 // PeerWithKey returns the Peer with key k and reports whether it was found.