cifs: use compounding for open and first query-dir for readdir()

Combine the initial SMB2_Open and the first SMB2_Query_Directory in a compound.
This shaves one round-trip of each directory listing, changing it from 4 to 3
for small directories.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>