device: send persistent keepalive when bringing up device

Reported-by: Marcelo Bello

device.go

@@ -138,6 +138,9 @@ func deviceUpdateState(device *Device) {
 		device.peers.RLock()
 		for _, peer := range device.peers.keyMap {
 			peer.Start()
+			if peer.persistentKeepaliveInterval > 0 {
+				peer.SendKeepalive()
+			}
 		}
 		device.peers.RUnlock()