Manually mark the link drained, such that if the receiver has requested the link be drained (as indicated by the
value of the {@link #getDrain()} flag) then any remaining credit is discarded and if necessary notice sent to the
receiver indicating it has been.
For use when {@link #isAutoDrained()} is false.
@return the number of credits actually discarded
@see #setAutoDrained(boolean)
Manually mark the link drained, such that if the receiver has requested the link be drained (as indicated by the value of the {@link #getDrain()} flag) then any remaining credit is discarded and if necessary notice sent to the receiver indicating it has been.
For use when {@link #isAutoDrained()} is false.
@return the number of credits actually discarded @see #setAutoDrained(boolean)