connectd: fix binding to same port on IPv4 and IPv6.

1. If the IPv6 address was public, that changed the wireaddr and thus the ipv4 bind
   would not be to a wildcard and would fail.
2. Binding two fds to the same port on both wildcard IPv4 and IPv6 succeeds; we only
   fail when we try to listen, so allow error at this point.

For some reason this triggered on my digital ocean machine.

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

tests/test_misc.py

@@ -3,7 +3,7 @@ from fixtures import *  # noqa: F401,F403
 from flaky import flaky
 from lightning import RpcError
 from utils import DEVELOPER, sync_blockheight, only_one, wait_for
-
+from ephemeral_port_reserve import reserve
 
 import json
 import os
@@ -772,3 +772,24 @@ def test_reserve_enforcement(node_factory, executor):
         'Peer permanent failure in CHANNELD_NORMAL: lightning_channeld: sent '
         'ERROR Bad peer_add_htlc: CHANNEL_ERR_CHANNEL_CAPACITY_EXCEEDED'
     )
+
+
+def test_ipv4_and_ipv6(node_factory):
+    """Test we can bind to both IPv4 and IPv6 addresses (if supported)"""
+    port = reserve()
+    l1 = node_factory.get_node(options={'addr': ':{}'.format(port)})
+    bind = l1.rpc.getinfo()['binding']
+
+    if len(bind) == 2:
+        assert bind[0]['type'] == 'ipv6'
+        assert bind[0]['address'] == '::'
+        assert int(bind[0]['port']) == port
+        assert bind[1]['type'] == 'ipv4'
+        assert bind[1]['address'] == '0.0.0.0'
+        assert int(bind[1]['port']) == port
+    else:
+        # Assume we're IPv4 only...
+        assert len(bind) == 1
+        assert bind[0]['type'] == 'ipv4'
+        assert bind[0]['address'] == '0.0.0.0'
+        assert int(bind[0]['port']) == port