VPN: Reload the tunnel before starting it up

To avoid errors like this: https://stackoverflow.com/q/47550706

WireGuard/WireGuard/VPN/TunnelsManager.swift

@@ -272,6 +272,8 @@ class TunnelContainer: NSObject {
                 s.status = .inactive
                 return
             }
+            s.tunnelProvider.loadFromPreferences { [weak s] (error) in
+                guard let s = s else { return }
                 s.startObservingTunnelStatus()
                 let session = (s.tunnelProvider.connection as! NETunnelProviderSession)
                 do {
@@ -284,6 +286,7 @@ class TunnelContainer: NSObject {
                 }
             }
         }
+    }
 
     fileprivate func startDeactivation() {
         assert(status == .active)