fix compilation of RRH GW

I am not sure this is the correct solution.

The problem seems to be that the RRH GW does not use ITTI
and thus the type 'as_nas_info_t' is not defined, and then
the compilation fails.

The simple fix is to include 'as_message.h' in
'openair2/RRC/LITE/defs.h' if ENABLE_ITTI is not
defined. Maybe it's not good. RRH GW compiles with this fix.

openair2/RRC/LITE/defs.h

@@ -102,6 +102,14 @@
 # include "intertask_interface.h"
 #endif
 
+/* TODO: be sure this include is correct.
+ * It solves a problem of compilation of the RRH GW,
+ * issue #186.
+ */
+#if !defined(ENABLE_ITTI)
+# include "as_message.h"
+#endif
+
 #if defined(ENABLE_USE_MME)
 # include "commonDef.h"
 #endif