Use explicit type casting to avoid sign extensions

Make sure sign extension does not end up getting used here by
explicitly type casting the variables to correct size.

Signed-hostap: Jouni Malinen <j@w1.fi>

src/eap_server/eap_server_ttls.c

@@ -98,7 +98,8 @@ static u8 * eap_ttls_avp_hdr(u8 *avphdr, u32 avp_code, u32 vendor_id,
 	}
 
 	avp->avp_code = host_to_be32(avp_code);
-	avp->avp_length = host_to_be32((flags << 24) | (hdrlen + len));
+	avp->avp_length = host_to_be32(((u32) flags << 24) |
+				       ((u32) (hdrlen + len)));
 
 	return avphdr + hdrlen;
 }