[v8.x] http: add maxHeaderSize property

-      const { getOptionValue } = require('internal/options');
-      maxHeaderSize = getOptionValue('--max-http-header-size');
+      maxHeaderSize = process.binding('config').maxHTTPHeaderSize;

internal/options does not exist on 8.x or 6.x. As such maxHTTPHeaderSize is exposed on process.binding('config')