get rid of numerous gcc-4 warnings
diff --git a/ip6tables.c b/ip6tables.c
index 9bfe1d3..49dcbf0 100644
--- a/ip6tables.c
+++ b/ip6tables.c
@@ -430,7 +430,8 @@
 }
 
 static void
-add_command(int *cmd, const int newcmd, const int othercmds, int invert)
+add_command(unsigned int *cmd, const int newcmd, const int othercmds,
+	    int invert)
 {
 	if (invert)
 		exit_error(PARAMETER_PROBLEM, "unexpected ! flag");