netem: fix loss 4 state model

Patch from developers of the alternative loss models, downloaded from:
   http://netgroup.uniroma2.it/twiki/bin/view.cgi/Main/NetemCLG



 "In the case 1 of the switch statement in the if conditions we
   need to add clg->a4 to clg->a1, according to the model."

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>