vi /etc/smb.conf

disable netbios = yes
smb ports = 445

Stop nmbd:

launchctl unload -w /System/Library/LaunchDaemons/nmbd.plist

Note: You may need to do the launchctl command a couple times. Not sure why but it did not always stop nmbd. Below is a portion of the nmbd.plist file. If set correctly to disable Netbios, you will see the KeepAlive instead of Enabled (the default).

nmbd.plist