6lowpan: add generic 6lowpan netdev private data

This patch introduced the 6lowpan netdev private data struct. We name it
lowpan_priv and it's placed at the beginning of netdev private data. All
lowpan interfaces should allocate this room at first of netdev private
data. 6LoWPAN LL private data can be allocate by additional netdev private
data, e.g. dev->priv_size should be "sizeof(struct lowpan_priv) +
sizeof(LL_LOWPAN_PRIVATE_DATA)".

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/6lowpan/core.c b/net/6lowpan/core.c
new file mode 100644
index 0000000..ed0eec9
--- /dev/null
+++ b/net/6lowpan/core.c
@@ -0,0 +1,20 @@
+/* This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Authors:
+ * (C) 2015 Pengutronix, Alexander Aring <aar@pengutronix.de>
+ */
+
+#include <net/6lowpan.h>
+
+void lowpan_netdev_setup(struct net_device *dev, enum lowpan_lltypes lltype)
+{
+	lowpan_priv(dev)->lltype = lltype;
+}
+EXPORT_SYMBOL(lowpan_netdev_setup);