MDL-56129 core: Change HTTP error code for iOS 10 video playback
MDL-56129 core: Change HTTP error code for iOS 10 video playback

This patch changes the effective response code from a 407 to a 403 when
erroring on iOS 10 and when a HTTP_X_PLAYBACK_SESSION_ID HTTP header is
found.

This causes the iOS Media framework to send the cookie with the request
which subsequently succeeds.

dilawar/moodle