A URL to be sent via a PADM on the sub-interface when this profile is
applied to the IP interface above this PPPoE sub-interface. The string
entered here can have several substitutions applied:
%D is replaced with the profile name
%d is replaced with the domain name
%u is replaced with the user name
%U is replaced with the user/domain name together
%% is replaced with the % character
The resulting string must not be greater than 127 octets long. The
client may use this URL as the initial web-page for the user.