NetworkExtension: close context before turning off go

The go turnOff code waits for all readers to have completed. In order to
make readers complete, we must send the signal to unblock the request.
Thus, we must reorder these.

WireGuard/WireGuardNetworkExtension/PacketTunnelProvider.swift

@@ -125,10 +125,10 @@ class PacketTunnelProvider: NEPacketTunnelProvider {
     /// Begin the process of stopping the tunnel.
     override func stopTunnel(with reason: NEProviderStopReason, completionHandler: @escaping () -> Void) {
         os_log("Stopping tunnel", log: OSLog.default, type: .info)
+        wgContext?.closeTunnel()
         if let handle = wgHandle {
             wgTurnOff(handle)
         }
-        wgContext?.closeTunnel()
         completionHandler()
     }