tests: Make proxy_test work on travis servers without IPv6

Github-Pull: #7489
Rebased-From: 7539f1aae3
Cherry-picked-From: 9ca957bcd4

qa/rpc-tests/test_framework/netutil.py

@@ -137,3 +137,18 @@ def addr_to_hex(addr):
     else:
         raise ValueError('Could not parse address %s' % addr)
     return binascii.hexlify(bytearray(addr))
+
+def test_ipv6_local():
+    '''
+    Check for (local) IPv6 support.
+    '''
+    import socket
+    # By using SOCK_DGRAM this will not actually make a connection, but it will
+    # fail if there is no route to IPv6 localhost.
+    have_ipv6 = True
+    try:
+        s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+        s.connect(('::1', 0))
+    except socket.error:
+        have_ipv6 = False
+    return have_ipv6