Add libnice and listen for direct connections in Jingle SOCKS5 (#608)

Add libnice as a plugin. If it is present, use libnice to enumerate
local IP addresses and listen on them to support direct connections for
Jingle SOCKS5.

Tested with Conversations and Gajim.

Created the nice.vapi file using
```
vapigen --library nice --pkg gio-2.0 --metadatadir metadata /usr/share/gir-1.0/Nice-0.1.gir
```

1 files changed, 15 insertions, 2 deletions

diff --git a/xmpp-vala/src/module/xep/0065_socks5_bytestreams.vala b/xmpp-vala/src/module/xep/0065_socks5_bytestreams.vala
index fdee2411..c184877c 100644
--- a/xmpp-vala/src/module/xep/0065_socks5_bytestreams.vala
+++ b/xmpp-vala/src/module/xep/0065_socks5_bytestreams.vala
@@ -18,21 +18,34 @@ public class Proxy : Object {
     }
 }
 
+public delegate Gee.List<string> GetLocalIpAddresses();
+
 public class Module : XmppStreamModule, Iq.Handler {
     public static Xmpp.ModuleIdentity<Module> IDENTITY = new Xmpp.ModuleIdentity<Module>(NS_URI, "0065_socks5_bytestreams");
 
+    private GetLocalIpAddresses? get_local_ip_addresses_impl = null;
+
     public override void attach(XmppStream stream) {
         stream.add_flag(new Flag());
         query_availability.begin(stream);
     }
     public override void detach(XmppStream stream) { }
 
-    public async void on_iq_set(XmppStream stream, Iq.Stanza iq) { }
-
     public Gee.List<Proxy> get_proxies(XmppStream stream) {
         return stream.get_flag(Flag.IDENTITY).proxies;
     }
 
+    public void set_local_ip_address_handler(owned GetLocalIpAddresses get_local_ip_addresses) {
+        get_local_ip_addresses_impl = (owned)get_local_ip_addresses;
+    }
+
+    public Gee.List<string> get_local_ip_addresses() {
+        if (get_local_ip_addresses_impl == null) {
+            return Gee.List.empty();
+        }
+        return get_local_ip_addresses_impl();
+    }
+
     private async void query_availability(XmppStream stream) {
         ServiceDiscovery.ItemsResult? items_result = yield stream.get_module(ServiceDiscovery.Module.IDENTITY).request_items(stream, stream.remote_name);
         if (items_result == null) return;