message: network-ntt: Add get_blocks stub
diff: @@ -198,6 +198,10 @@ where
  }
  }
  + fn get_blocks(&mut self, _ids: &[<Self::Block as Block>::Id]) -> Self::GetBlocksFuture {
  + unimplemented!()
  + }
  +
  fn block_subscription<Out>(&mut self, _outbound: Out) -> Self::BlockSubscriptionFuture
  where
  Out: Stream<Item = T::Header>,
  