[3328] Change Dhcp6 spec file so D2 server IP address matches Dhcp4

Out of the box both DHCP servers should look at the same defualt address
for D2, as D2 only opens one ip/port (currently).

src/bin/dhcp6/dhcp6.spec

@@ -382,7 +382,7 @@
                 "item_name": "server-ip",
                 "item_type": "string",
                 "item_optional": true,
-                "item_default": "::1",
+                "item_default": "127.0.0.1",
                 "item_description" : "IP address of b10-dhcp-ddns (IPv4 or IPv6)"
             },
             {