Provide SMB option to support Windows 2000

As of SAMBA 4.11 (https://www.samba.org/samba/history/samba-4.11.0.html), SMB1 is disabled by default (and may be removed in the future). This breaks SMB shares with Windows 2000 guests.

Adding the following line to smb.conf fixes this:

min protocol = NT1

I would propose that an option be added to add this line to smb.conf to support these legacy operating systems.