CURLOPT_POSTFIELDSIZE_LARGE(3) on macOS

The text 814c51a60ec9, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

size of POST data pointed to

CURLOPT_POSTFIELDSIZE_LARGE(3) on macOS now