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
```

2 files changed, 33 insertions, 0 deletions

diff --git a/plugins/ice/src/plugin.vala b/plugins/ice/src/plugin.vala
new file mode 100644
index 00000000..f1c41a27
--- /dev/null
+++ b/plugins/ice/src/plugin.vala
@@ -0,0 +1,30 @@
+using Gee;
+using Nice;
+using Xmpp;
+
+namespace Dino.Plugins.Ice {
+
+public class Plugin : RootInterface, Object {
+    public Dino.Application app;
+
+    public void registered(Dino.Application app) {
+        this.app = app;
+        app.stream_interactor.stream_attached_modules.connect((account, stream) => {
+            stream.get_module(Xmpp.Xep.Socks5Bytestreams.Module.IDENTITY).set_local_ip_address_handler(get_local_ip_addresses);
+        });
+    }
+
+    private Gee.List<string> get_local_ip_addresses() {
+        Gee.List<string> result = new ArrayList<string>();
+        foreach (string ip_address in Nice.interfaces_get_local_ips(false)) {
+            result.add(ip_address);
+        }
+        return result;
+    }
+
+    public void shutdown() {
+        // Nothing to do
+    }
+}
+
+}
diff --git a/plugins/ice/src/register_plugin.vala b/plugins/ice/src/register_plugin.vala
new file mode 100644
index 00000000..b2ed56c1
--- /dev/null
+++ b/plugins/ice/src/register_plugin.vala
@@ -0,0 +1,3 @@
+public Type register_plugin(Module module) {
+    return typeof (Dino.Plugins.Ice.Plugin);
+}