Test |ECDSA_SIG_to_bytes| using the P-521 order size, not 512-bits.

There was a test for 512 bit orders but not one for 521-bit orders.
Test 521-bit orders instead.

Change-Id: I61a76d02637ca55d8ae21834085311dd84fd870f
Reviewed-on: https://boringssl-review.googlesource.com/7011
Reviewed-by: David Benjamin <davidben@google.com>

crypto/ecdsa/ecdsa_test.cc

@@ -340,15 +340,19 @@ static bool TestECDSA_SIG_max_len(size_t order_len) {
   return true;
 }
 
+static size_t BitsToBytes(size_t bits) {
+  return (bits / 8) + (7 + (bits % 8)) / 8;
+}
+
 int main(void) {
   CRYPTO_library_init();
 
   if (!TestBuiltin(stdout) ||
-      !TestECDSA_SIG_max_len(224/8) ||
-      !TestECDSA_SIG_max_len(256/8) ||
-      !TestECDSA_SIG_max_len(384/8) ||
-      !TestECDSA_SIG_max_len(512/8) ||
-      !TestECDSA_SIG_max_len(10000)) {
+      !TestECDSA_SIG_max_len(BitsToBytes(224)) ||
+      !TestECDSA_SIG_max_len(BitsToBytes(256)) ||
+      !TestECDSA_SIG_max_len(BitsToBytes(384)) ||
+      !TestECDSA_SIG_max_len(BitsToBytes(521)) ||
+      !TestECDSA_SIG_max_len(BitsToBytes(10000))) {
     printf("\nECDSA test failed\n");
     ERR_print_errors_fp(stdout);
     return 1;