The value of the object tmnxLocUsrDbPppoeMaskPreNum specifies
the number of characters to remove from the start of the incoming
string before it is matched against the value configured in the
corresponding object in the tmnxLocUsrDbPppoeTable.
At least one of the values of tmnxLocUsrDbPppoeMaskPreNum and
tmnxLocUsrDbPppoeMaskPreStr must be equal to the default value.