smb: client: extend smb2_compound_op() to accept more commands

Make smb2_compound_op() accept up to MAX_COMPOUND(5) commands to be
sent over a single compounded request.

This will allow next commits to read and write reparse files through a
single roundtrip to the server.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>