Adjust thread index type to uint16 for future expansion & Organize stellar directory files

src/packet/packet_priv.h

@@ -69,6 +69,8 @@ void *packet_get_io_ctx(const struct packet *pkt);
 
 int packet_is_fragment(const struct packet *pkt);
 
+void packet_set_ctrl(struct packet *pkt);
+
 struct packet *packet_new(uint16_t pkt_len);
 void packet_free(struct packet *pkt);
 struct packet *packet_dup(const struct packet *pkt);