s4:tortore:raw/qfileinfo: don't use dcerpc_pipe_open_smb() to open a named pipe

We can directly use smb_raw_open() to open a handle to a named pipe.
This avoids the need for the layer violation functions
dcerpc_smb_tree() and dcerpc_smb_fnum().

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>