funding: don't allow funding new channels until we're synced.

This is probably worth preventing.

1. Our depth estimate would be inaccurate possibly leading to us
   timing out too early.
2. If we're not up-to-date our onchain funds are unknown.
3. We wouldn't be able to send or receive HTLCs until we're synced anyway.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_misc.py

@@ -152,16 +152,22 @@ def test_lightningd_still_loading(node_factory, bitcoind, executor):
             "id": r['id']
         }
 
-    # Start it, establish channel.
+    # Start it, establish channel, get extra funds.
     l1, l2 = node_factory.line_graph(2, opts={'may_reconnect': True})
-    # Balance channel.
+    # Extra funds, for second channel attempt.
+    bitcoind.rpc.sendtoaddress(l1.rpc.newaddr()['bech32'], 1.0)
+    # Balance l1<->l2 channel
     l1.pay(l2, 10**9 // 2)
+
     l1.stop()
 
+    # Start extra node.
+    l3 = node_factory.get_node()
+
     # Now make sure it's behind.
     bitcoind.generate_block(2)
-    # Make sure l2 is synced
-    sync_blockheight(bitcoind, [l2])
+    # Make sure l2/l3 are synced
+    sync_blockheight(bitcoind, [l2, l3])
 
     # Make it slow grabbing the final block.
     slow_blockid = bitcoind.rpc.getblockhash(bitcoind.rpc.getblockcount())
@@ -177,6 +183,11 @@ def test_lightningd_still_loading(node_factory, bitcoind, executor):
     with pytest.raises(RpcError, match=r'TEMPORARY_CHANNEL_FAILURE'):
         l1.pay(l2, 1000)
 
+    # Can't fund a new channel, either.
+    l1.rpc.connect(l3.info['id'], 'localhost', l3.port)
+    with pytest.raises(RpcError, match=r'304'):
+        l1.rpc.fundchannel(l3.info['id'], 'all')
+
     # This will work, but will be delayed until synced.
     fut = executor.submit(l2.pay, l1, 1000)
     l1.daemon.wait_for_log("Deferring incoming commit until we sync")