tls: using %StringSplit to split `cert.subjectaltname`

There are 2 changes in this patch:

* using `%StringSplit` not `StringSplitOnRegExp` in [v8/v8](https://github.com/v8/v8/blob/master/src/string.js#L588), the newer function seems to be faster.

* decreasing the times of comparing regular expression, and more readable for human.
if (option[1] === 'DNS') {