leak-detective: Also ignore unknown memory freed in OPENSSL_cleanup()

It seems that 18a94525a7 was a bit hasty.  Apparently, it's still the
case that there were reports (at least in some test scenarios).  Luckily,
the new facility added in the previous commit allows us to whitelist
these allocations without having to ignore all unknown memory.

src/libstrongswan/utils/leak_detective.c

@@ -680,6 +680,7 @@ static char *whitelist[] = {
  */
 static char *unknown_memory_whitelist[] = {
 	"tzset",
+	"OPENSSL_cleanup",
 };
 
 /**