DvInfo Data may exceed the link MTU

[italovalcy]

When encoding the Distance Vector information Data, we need to take care of the MTU to avoid exceeding and get error or bad behavior:

+567.631392993s 6 ndn.Ndvr:OnDvInfoInterest(): [INFO ] Replying DV-Info with encoded data: size=8716 I=/ndvr/dvinfo/ndn/%C1.Router/Router6/%027
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<ndn::Face::OversizedPacketError> >'
  what():  Data /ndvr/dvinfo/ndn/%C1.Router/Router6/%027 encodes into 8895 octets, exceeding the implementation limit of 8800 octets

In the above case, node 6 has more than 240 routes and the total size of encoded data was 8716 (num_routes * (length_name_prefix + len(seqNum+cost))).