bssgp: Increment BSSGP flow control tag value

Currently the tag value in FLOW CONTROL BVC messages is always 1.

This commit changes the implementation to increment that value with
each of the FLOW CONTROL BVC messages that is sent to the SGSN.

Sponsored-by: On-Waves ehf

src/gprs_bssgp_pcu.cpp

@@ -642,13 +642,16 @@ int gprs_bssgp_tx_fc_bvc(void)
 	/* Avg queue delay monitoring */
 	avg_delay_ms = get_and_reset_avg_queue_delay();
 
+	/* Update tag */
+	the_pcu.fc_tag += 1;
+
 	LOGP(DBSSGP, LOGL_DEBUG,
 		"Sending FLOW CONTROL BVC, Bmax = %d, R = %d, Bmax_MS = %d, "
 		"R_MS = %d, avg_dly = %d\n",
 		bucket_size, leak_rate, ms_bucket_size, ms_leak_rate,
 		avg_delay_ms);
 
-	return bssgp_tx_fc_bvc(the_pcu.bctx, 1,
+	return bssgp_tx_fc_bvc(the_pcu.bctx, the_pcu.fc_tag,
 		bucket_size, leak_rate,
 		ms_bucket_size, ms_leak_rate,
 		NULL, &avg_delay_ms);

src/gprs_bssgp_pcu.h

@@ -61,6 +61,7 @@ struct gprs_bssgp_pcu {
 	/* Flow control */
 	struct timeval queue_delay_sum;
 	unsigned queue_delay_count;
+	uint8_t fc_tag;
 
 	/** callbacks below */