libvlc: fix network media parsing

Calls to `libvlc_media_parse_request` with smb server URL never succeeded
because `do_parse` var was always `false` when `input_net` var was `true`
and `libvlc_media_parse_network` flag was set.

This change fixes this problem and bring back the ability to parse network
files when the `libvlc_media_parse_network` flag is set