gprs_ns2: add member name to bind

Every bind will have a unique name. Add a name argument
to all bind creating functions and require them to be unique.

This is an API break but there wasn't yet a release with NS2.

Change-Id: I8f1d66b7b3b12da12db8b5e6bd08c1beff085b3e
diff --git a/src/gb/gprs_ns2_internal.h b/src/gb/gprs_ns2_internal.h
index 8c0c135..9bfe0b0 100644
--- a/src/gb/gprs_ns2_internal.h
+++ b/src/gb/gprs_ns2_internal.h
@@ -181,6 +181,8 @@
 
 /*! Structure repesenting a bind instance. E.g. IPv4 listen port. */
 struct gprs_ns2_vc_bind {
+	/*! unique name */
+	const char *name;
 	/*! list entry in nsi */
 	struct llist_head list;
 	/*! list of all VC */