The value of tmnxRadProxSrvLoadBalanceKey specifies
how to construct the key for load-balancing RADIUS messages
between RADIUS servers.
The value 'none' specifies that there be no load-balancing.
The value 'sourceIpUdp' specifies that the key consists of
the source IP address and source UDP port of the RADIUS message.
The value 'attributes' specifies that the key is constructed with the
attributes in the RADIUS message listed in the objects
tmnxRadProxSrvLoadBAttr1 to tmnxRadProxSrvLoadBAttr5.