vfs: Change SMB_VFS_DISK_FREE to take a fsp

vfs: Change SMB_VFS_DISK_FREE to take a fsp

The modules that change the pathname need a synthetic_pathref now for
the SMB_VFS_NEXT_DISK_FREE() call. I think this is the right thing to
do anyway, as this goes through all the path scrutiny and does not
depend on direct multi-component paths anymore.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Anoop C S <anoopcs@samba.org>