Port Queue to C++

Some knock-on changes to keep a simple design:
- Bake the data array into AVCLAN_frame_t
- Bundle the response/reaction with AVCLAN_frame_t
    - (Needed to maintain correct/simple ownership semantics with the
      cache and outgoing/incoming queues)
- Switch status frame update ticks to use a regular
  cache-originating/owned frame

src/avclan/avclan_defs.h

@@ -116,12 +116,13 @@ typedef struct print_struct {
 } log_t;
 
 typedef struct AVCLAN_frame_struct {
+  uint8_t reaction;
   bool is_unicast;
   uint16_t controller_addr; // formerly "master"
   uint16_t peripheral_addr; // formerly "slave"
   uint8_t control;
   uint8_t length;
-  uint8_t *data;
+  uint8_t data[MAXMSGLEN];
 } AVCLAN_frame_t;
 
 // A single bus symbol. bit_zero/bit_one carry data (and double as parity