Split backend and outgoing. Rename backend -> receive, client -> send.

common.h

@@ -44,7 +44,6 @@ void buf_consume(struct buf *, size_t);
 //////// packet
 
 #define DATA_LEN_MAX 14
-struct backend;
 struct packet {
 	enum {
 		MODE_S_SHORT,
@@ -54,7 +53,6 @@ struct packet {
 	uint8_t payload[DATA_LEN_MAX];
 	uint64_t mlat_timestamp;
 	uint32_t rssi;
-	struct backend *backend;
 };
 extern char *packet_type_names[];