gprs_ns2: don't use llist_for_each when freeing an element

The problem are recursive execution because a free generates an event which could
allow the use to free a nsvcs while the llist_for_each() is still running.

Change-Id: I902557fb6e56e6588728a46e43a9cbe3215d5c68
diff --git a/src/gb/gprs_ns2_internal.h b/src/gb/gprs_ns2_internal.h
index d2407f6..ca6bfb7 100644
--- a/src/gb/gprs_ns2_internal.h
+++ b/src/gb/gprs_ns2_internal.h
@@ -354,6 +354,7 @@
 				 enum gprs_ns2_vc_mode vc_mode,
 				 const char *id);
 
+void ns2_free_nsvcs(struct gprs_ns2_nse *nse);
 int ns2_bind_alloc(struct gprs_ns2_inst *nsi, const char *name,
 		   struct gprs_ns2_vc_bind **result);