ContikiMAC: Create and parse ContikiMAC header in special framer; Expanded framer interface

to allow for creating and securing frames in advance; Create and secure frames in advance when sending bursts; Do neither recreate nor resecure frames that come from phase

core/net/mac/framer-nullmac.c

@@ -97,5 +97,8 @@ parse(void)
 }
 /*---------------------------------------------------------------------------*/
 const struct framer framer_nullmac = {
-  hdr_length, create, parse
+  hdr_length,
+  create,
+  framer_canonical_create_and_secure,
+  parse
 };