vty: Inform user that static IP addresses are not supported

Currently, osmo-ggsn doesn't implement PDP contexts with static IP
addresses.  The code for specifying ranges that can be used for
static IPs was always present even from OpenGGSN days, but we never
really treated them.  Let's not raise the impression we do by
warning accordingly if the user configures them.

Change-Id: I7787dae037c46c0c5052aa6dd000be330984f144
Related: OS#5097
diff --git a/ggsn/ggsn_vty.c b/ggsn/ggsn_vty.c
index 71d8ff6..1738e70 100644
--- a/ggsn/ggsn_vty.c
+++ b/ggsn/ggsn_vty.c
@@ -533,9 +533,11 @@
 	struct in46_prefix *pfx;
 
 	/* first update our parsed prefix */
-	if (!strcmp(argv[0], "static"))
+	if (!strcmp(argv[0], "static")) {
 		pfx = &apn->v4.cfg.static_prefix;
-	else
+		vty_out(vty, "%% static IP addresses currently not yet supported%s", VTY_NEWLINE);
+		return CMD_WARNING;
+	} else
 		pfx = &apn->v4.cfg.dynamic_prefix;
 	str2prefix(pfx, argv[1]);
 
@@ -567,9 +569,11 @@
 	struct apn_ctx *apn = (struct apn_ctx *) vty->index;
 	struct in46_prefix *pfx;
 
-	if (!strcmp(argv[0], "static"))
+	if (!strcmp(argv[0], "static")) {
 		pfx = &apn->v6.cfg.static_prefix;
-	else
+		vty_out(vty, "%% static IP addresses currently not yet supported%s", VTY_NEWLINE);
+		return CMD_WARNING;
+	} else
 		pfx = &apn->v6.cfg.dynamic_prefix;
 	str2prefix(pfx, argv[1]);
 	return CMD_SUCCESS;