l3 doesn't just need to know about l2 (which it can get from the
channel_announcement), but needs to see the node_announcement.
Otherwise:
```
l1, l2 = node_factory.line_graph(2, wait_for_announce=True,
# No onion_message support in l1
opts=[{'dev-force-features': -39},
{'dev-allow-localhost': None}])
l3 = node_factory.get_node()
l3.rpc.connect(l1.info['id'], 'localhost', l1.port)
wait_for(lambda: l3.rpc.listnodes(l2.info['id'])['nodes'] != [])
offer = l2.rpc.call('offer', {'amount': '2msat',
'description': 'simple test'})
> l3.rpc.call('fetchinvoice', {'offer': offer['bolt12']})
tests/test_pay.py:4804:
...
> raise RpcError(method, payload, resp['error'])
E pyln.client.lightning.RpcError: RPC call failed: method: fetchinvoice, payload: {'offer': 'lno1qgsqvgnwgcg35z6ee2h3yczraddm72xrfua9uve2rlrm9deu7xyfzrcgqypq5zmnd9khqmr9yp6x2um5zcssxwz9sqkjtd8qwnx06lxckvu6g8w8t0ue0zsrfqqygj636s4sw7v6'}, error: {'code': 1003, 'message': 'Failed: could not route or connect directly to 033845802d25b4e074ccfd7cd8b339a41dc75bf9978a034800444b51d42b07799a: {"code":400,"message":"Unable to connect, no address known for peer"}'}
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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