[Samba] dfree hardcoded limitation

[J. Douglas]

I would like to make my readonly shares report 0 free space.

But, smbd/dfree.c hardcodes min limits, preventing me from using 0 in my dfree 
command.  Is there a reason for this? Can it be removed?

 if (!*dsize)
   *dsize = 2048;
 if (!*dfree)
   *dfree = 1024;