NLSR

Currently, NLSR only reacts to when a Face is destroyed. Since HelloProtocol effectively diagnoses it, NLSR does not waste too much time if a Face goes down. However, when a Face comes back up, NLSR does not react to it in any way. This means there is a long period, before the next HelloInterval, where NLSR is possibly ignoring a neighbor. Fixing this would improve performance. NLSR should react accordingly based on whether the Face is permanent or ephemeral.