The value of the object tmnxLocUsrDbPppoeMaskPreStr specifies
a substring that is stripped off the start of the incoming string
before it is matched against the value configured in the corresponding
object in the tmnxLocUsrDbPppoeTable.
This string can only contain printable ASCII characters.
Character '*' is a wildcard that matches any substring; it can be
escaped by character '\'.
At least one of the values of tmnxLocUsrDbPppoeMaskPreNum and
tmnxLocUsrDbPppoeMaskPreStr must be equal to the default value.