Add tun.[ch]

src/tun.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <unistd.h>
+
+int     tun_create (char *, int);
+ssize_t tun_read   (int, void *, size_t);
+ssize_t tun_write  (int, const void *, size_t);