Missing nsmb.conf file
Just create the file via commandline/Terminal. It does not exist by default. 

sudo touch /etc/nsmb.conf


The smb.conf file is most likely carried over from updating older versions of macOS. It’s not used anymore in Mojave.

The terminal command above is the global location for the config file, if you want to set config options for specific users, see the following URL. The link also contains additional info about SMB config.

https://www.flyweb.at/blog/network/1004/samba-fun-with-osx/