tc: fix compilation warning on 32bits arch

The warning was:
m_simple.c: In function ‘parse_simple’:
m_simple.c:142:4: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 3 has type ‘size_t’ [-Wformat]

Useful to be able to compile with -Werror.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>

tc/m_simple.c

@@ -138,7 +138,7 @@ parse_simple(struct action_util *a, int *argc_p, char ***argv_p, int tca_id,
 	}
 
 	if (strlen(simpdata) > (SIMP_MAX_DATA - 1)) {
-		fprintf(stderr, "simple: Illegal string len %ld <%s> \n",
+		fprintf(stderr, "simple: Illegal string len %zu <%s> \n",
 			strlen(simpdata), simpdata);
 		return -1;
 	}