MEDIUM: protocol: add minimalist UDP protocol client

Basic introduction of a UDP layer in HAProxy. It can be used as a
client only and manages UDP exchanges with servers.

It can't be used to load-balance UDP protocols, but only used by
internal features such as DNS resolution.
diff --git a/src/proto_udp.c b/src/proto_udp.c
new file mode 100644
index 0000000..0e361d9
--- /dev/null
+++ b/src/proto_udp.c
@@ -0,0 +1,33 @@
+/*
+ * UDP protocol related functions
+ *
+ * Copyright 2014 Baptiste Assmann <bedis9@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <types/global.h>
+#include <types/fd.h>
+#include <types/proto_udp.h>
+
+#include <proto/fd.h>
+
+/* datagram handler callback */
+int dgram_fd_handler(int fd)
+{
+	struct dgram_conn *dgram = fdtab[fd].owner;
+
+	if (unlikely(!dgram))
+		return 0;
+
+	if (fd_recv_ready(fd))
+		dgram->data->recv(dgram);
+	else if (fd_send_ready(fd))
+		dgram->data->send(dgram);
+
+	return 0;
+}