Configured Transmit Buffer Credits. Values other than zero over-ride
the router selected values. A value of zero has a special meaning.
Zero causes router based default values to be used. All values are
accepted. Care should be taken not to set this to a value which is
much greater than the default. The default can be read out of the
wfDs1E1ModuleTxBufferUseCredits attribute when the router is
running with this attribute set to zero. Sets to this attribute
may take up to one minute to take effect.