pytest: fix flake in test_wumbo_channels

We need to wait for *l2* to see the channel in CHANNELD_NORMAL,
otherwise the array here is empty:

```
	chan = only_one([c for c in l1.rpc.listpeerchannels(l2.info['id'])['channels'] if c['state'] == 'CHANNELD_NORMAL'])
        amount = chan['funding']['local_funds_msat']
        assert amount > Millisatoshi(str((1 << 24) - 1) + "sat")
    
        # We should know we can spend that much!
        spendable = chan['spendable_msat']
        assert spendable > Millisatoshi(str((1 << 24) - 1) + "sat")
    
        # So should peer.
>       chan = only_one([c for c in l2.rpc.listpeerchannels(l1.info['id'])['channels'] if c['state'] == 'CHANNELD_NORMAL'])

tests/test_connection.py:3552: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

arr = []

    def only_one(arr):
        """Many JSON RPC calls return an array; often we only expect a single entry
        """
>       assert len(arr) == 1
E       AssertionError
```

Author: rustyrussell

tests/test_connection.py

@@ -3533,11 +3533,13 @@ def test_wumbo_channels(node_factory, bitcoind):
     l1.rpc.close(l2.info['id'])
     bitcoind.generate_block(1, wait_for_mempool=1)
     wait_for(lambda: l1.channel_state(l2) == 'ONCHAIN')
+    wait_for(lambda: l2.channel_state(l1) == 'ONCHAIN')
 
     l1.rpc.connect(l2.info['id'], 'localhost', port=l2.port)
     l1.rpc.fundchannel(l2.info['id'], 'all')
     bitcoind.generate_block(1, wait_for_mempool=1)
     wait_for(lambda: 'CHANNELD_NORMAL' in [c['state'] for c in l1.rpc.listpeerchannels(l2.info['id'])['channels']])
+    wait_for(lambda: 'CHANNELD_NORMAL' in [c['state'] for c in l2.rpc.listpeerchannels(l1.info['id'])['channels']])
 
     # Exact amount depends on fees, but it will be wumbo!
     chan = only_one([c for c in l1.rpc.listpeerchannels(l2.info['id'])['channels'] if c['state'] == 'CHANNELD_NORMAL'])