Added IP pdu class. It's compiling so far.

include/utils.h

@@ -0,0 +1,16 @@
+#ifndef __UTILS_H
+#define __UTILS_H
+
+
+#include <string>
+#include <stdint.h>
+
+namespace Tins {
+    /* Utils namespace. */
+    namespace Utils {
+        uint32_t ip_to_int(const std::string &ip);
+        std::string ip_to_string(uint32_t ip);
+    };
+};
+
+#endif