connection: handle ACKs from empty packets correctly

impl/src/layer2/connection.c

@@ -114,6 +114,8 @@ result_t connection_handle_packet(connection_ctx_t *ctx, const uint8_t *buf, siz
 	switch(header.msg_type) {
 		case L2_MSG_TYPE_EMPTY:
 			LOG(LVL_DEBUG, "Empty packet: accepted ACK for %u.", ctx->last_acked_seq);
+			// handle the acknowledgement internally
+			connection_handle_ack(ctx, header.rx_seq_nr);
 			return OK; // do not ACK and call back
 
 		case L2_MSG_TYPE_CONN_MGMT: