Fail to apply gossip update for invalid chain hash

[tnull]

Currently, NetworkGraph::update_channel_unsigned and similar methods will happily apply updates, even if they don't match its genesis_hash. This for example happens when syncing a testnet graph with the mainnet RGS url.

However, we should check the given chain hash in NetworkGraph::update_channel_intern and refuse to apply any updates that don't match the network we're on.

[freddiekrugerrand]

I'd like to pick this up if it's available!