update mods-available:sql suggestion

[Jonathan]

In order to standardize configuration more, we could just use below default
configuration:



+++ /etc/freeradius/mods-available/sql 2020-03-03 16:09:11.306618514 +0100
@@ -30,6 +30,7 @@
        #
        #  Allowed dialects are:
        #
+       #       null
        #       mssql
        #       mysql
        #       oracle
@@ -37,7 +38,7 @@
        #       sqlite
        #       mongo
        #
-       dialect = "sqlite"
+       dialect = "null"

        #
        #  The driver module used to execute the queries.  Since we
@@ -58,8 +59,7 @@
        #       rlm_sql_unixodbc
        #       rlm_sql_mongo
        #
-       driver = "rlm_sql_null"
-#      driver = "rlm_sql_${dialect}"
+       driver = "rlm_sql_${dialect}"