The value of tmnxRadProxUsrToRspMatchString specifies
the characters to match with the first characters in
the RADIUS User-Name attribute.
For example, a value of '20620' matches a RADIUS
User-Name '206200487175230' and '206200486514245', but
not '206010476405285' or '206010476420620'.
A value for this object must be specified when the row is created.