bssgp: introduce flush queue functions

To reset the state of BSSGP allow to flush the BSSGP queues.
When testing (with TTCN3) the test object should be resetted between
each test.

Introduce the functions:
bssgp_fc_flush_queue() - flushs a single flow control object
bssgp_flush_all_queues() - flushs queues of all BSSGP connections

Change-Id: I29b6ad6742ddf9b0b58b4af37d9a1cf18e019325
diff --git a/include/osmocom/gprs/gprs_bssgp.h b/include/osmocom/gprs/gprs_bssgp.h
index 2dead69..400c3e0 100644
--- a/include/osmocom/gprs/gprs_bssgp.h
+++ b/include/osmocom/gprs/gprs_bssgp.h
@@ -207,6 +207,9 @@
 int bssgp_fc_ms_init(struct bssgp_flow_control *fc_ms, uint16_t bvci,
 		     uint16_t nsei, uint32_t max_queue_depth);
 
+void bssgp_flush_all_queues();
+void bssgp_fc_flush_queue(struct bssgp_flow_control *fc);
+
 /* gprs_bssgp_vty.c */
 int bssgp_vty_init(void);
 void bssgp_set_log_ss(int ss);