The value of tmnxSubAuthPlcyUserNameMacFormat specifies how a MAC
address is represented when contacting a RADIUS server.
This is only used while the value of tmnxSubAuthPlcyUserNameFormat is
equal to 'dhcpClientVendorOpts' and if the MAC address is used
by default of DHCP client vendor options.
Examples:
'ab:' 00:0c:f1:99:85:b8 Alcatel-Lucent SROS style
'XY-' 00-0C-F1-99-85-B8 IEEE canonical style
'mmmm.' 0002.03aa.abff Cisco style.