cifs: add SMB2_open() arg to return POSIX data

allows SMB2_open() callers to pass down a POSIX data buffer that will
trigger requesting POSIX create context and parsing the response into
the provided buffer.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>