Updated protocol defaults to SMB2 minimum per upstream.

Upstream, Samba, has long since changed the defaults to SMB2 for client and server due to major security issues in the SMB1/CIFS/NT1 protocol. This adjustment reverts the manual change to NT1 previously back to current standards, and thanks to previous commits doesn't clobber the smb.conf changes users have already made, allowing them to transition accordingly on their own.