return empty string if ip4s is undefined in FireRouter.enrighWanStatus
return empty string if ip4s is undefined in FireRouter.enrighWanStatus

MelvinTo/firewalla,MelvinTo/firewalla,MelvinTo/firewalla,firewalla/firewalla,MelvinTo/firewalla,firewalla/firewalla,firewalla/firewalla,firewalla/firewalla,MelvinTo/firewalla,firewalla/firewalla