s3: smbd: Change dptr_create() to take a const struct smb_filename * instead of const...

s3: smbd: Change dptr_create() to take a const struct smb_filename * instead of const char *.

Also internally change path storage inside struct dptr_struct
to a struct smb_filename *.

This allows me to remove several of the synthetic_smb_fname()
calls I had to add in the previous patches, as we're now
dealing with struct smb_filename * throughout the dptr and
OpenDir code.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Mar  1 18:34:24 CET 2016 on sn-devel-144