lib/nlattr.c: Fix warning due to incorrect strlen() variable type

strlen() returns a size_t, not an int.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Change-Id: If5b0e3eb9d237f88ae96301ca4736c08ffe139cc

lib/nlattr.c

@@ -374,7 +374,7 @@ EXPORT_SYMBOL(nla_memcmp);
  */
 int nla_strcmp(const struct nlattr *nla, const char *str)
 {
-	int len = strlen(str);
+	size_t len = strlen(str);
 	char *buf = nla_data(nla);
 	int attrlen = nla_len(nla);
 	int d;