action: typo nat fix

If you taketh you giveth.
I Went the LinuxWay and copied this for m_simple.c and noticed
this one typo (I wonder where it came from?;->).

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
diff --git a/tc/m_nat.c b/tc/m_nat.c
index 01ec032..d502a81 100644
--- a/tc/m_nat.c
+++ b/tc/m_nat.c
@@ -146,7 +146,7 @@
 		if (matches(*argv, "index") == 0) {
 			NEXT_ARG();
 			if (get_u32(&sel.index, *argv, 10)) {
-				fprintf(stderr, "Pedit: Illegal \"index\"\n");
+				fprintf(stderr, "Nat: Illegal \"index\"\n");
 				return -1;
 			}
 			argc--;