mariadb: fix binding to 127.0.0.1 by default

[makigumo]

Currently the configuration to bind the server to 127.0.0.1 is not applied correctly.

This is because following the installation process there will be already a my.cnf file before installing the my.cnf file containing the bind-address configuration. Thus keeping the first my.cnf and installing to my.cnf.default instead.

To fix this issue, install to bind-address configuration file to my.cnf.d/ instead.