ggsn_vty.c: Print ipv6 link-local cmd when writing config to file

Previous commit added the ipv6 link-local vty cmd but forgot to add code
to print its value in config_write_apn.

Fixes: 37c45e3998fca240b5266abd3ac883d0a35bab50

Change-Id: I08aeaa98d6dc318b7e9740d837ba4ac48cd7051c
diff --git a/ggsn/ggsn_vty.c b/ggsn/ggsn_vty.c
index db392fa..6ddfc0d 100644
--- a/ggsn/ggsn_vty.c
+++ b/ggsn/ggsn_vty.c
@@ -686,6 +686,8 @@
 	}
 	if (apn->v6.cfg.ifconfig_prefix.addr.len)
 		vty_dump_prefix(vty, "  ipv6 ifconfig", &apn->v6.cfg.ifconfig_prefix);
+	if (apn->v6.cfg.ll_prefix.addr.len)
+		vty_dump_prefix(vty, "  ipv6 link-local", &apn->v6.cfg.ll_prefix);
 
 	/* must be last */
 	vty_out(vty, "  %sshutdown%s", apn->cfg.shutdown ? "" : "no ", VTY_NEWLINE);