moved sixlowpan into network_layer subfolder

sys/Makefile

@@ -65,7 +65,7 @@ ifneq (,$(findstring protocol_multiplex,$(USEMODULE)))
     DIRS += net/link_layer/protocol-multiplex
 endif
 ifneq (,$(findstring sixlowpan,$(USEMODULE)))
-    DIRS += net/sixlowpan
+    DIRS += net/network_layer/sixlowpan
 endif
 ifneq (,$(findstring rpl,$(USEMODULE)))
     DIRS += net/routing/rpl

sys/net/include/ipv6.h

@@ -23,7 +23,7 @@
 #include "sixlowpan/icmp.h"
 #include "sixlowpan/ndp.h"
 
-#include "../sixlowpan/icmp.h"        /* TODO: remove if not needed anymore */
+#include "../network_layer/sixlowpan/icmp.h"        /* TODO: remove if not needed anymore */
 
 /**
  * @}