gprs_ns2: add gprs_ns2_free_binds() to free all binds

Allow users to clean up all binds (e.g. the PCU).

Change-Id: Ic8f6f8aca10da23a18fab8870be7806065a34b47
diff --git a/include/osmocom/gprs/gprs_ns2.h b/include/osmocom/gprs/gprs_ns2.h
index d798ac4..2c58723 100644
--- a/include/osmocom/gprs/gprs_ns2.h
+++ b/include/osmocom/gprs/gprs_ns2.h
@@ -131,6 +131,7 @@
 					uint16_t nsvci);
 
 void gprs_ns2_free_bind(struct gprs_ns2_vc_bind *bind);
+void gprs_ns2_free_binds(struct gprs_ns2_inst *nsi);
 
 /* create a VC SNS connection */
 int gprs_ns2_ip_connect_sns(struct gprs_ns2_vc_bind *bind,