gprs_ns2: add gprs_ns2_free_nsvcs() to free all NS-VC of a NSE

Change-Id: I909443b540dbf75146297f1d7f94940690be6c0d
diff --git a/include/osmocom/gprs/gprs_ns2.h b/include/osmocom/gprs/gprs_ns2.h
index 41587d3..00879d7 100644
--- a/include/osmocom/gprs/gprs_ns2.h
+++ b/include/osmocom/gprs/gprs_ns2.h
@@ -160,6 +160,7 @@
 
 /* create vc */
 void gprs_ns2_free_nsvc(struct gprs_ns2_vc *nsvc);
+void gprs_ns2_free_nsvcs(struct gprs_ns2_nse *nse);
 struct gprs_ns2_vc *gprs_ns2_nsvc_by_nsvci(struct gprs_ns2_inst *nsi, uint16_t nsvci);
 
 /* generic VL driver */