netxen: fix netxen_nic_poll() logic

NAPI poll logic now enforces that a poller returns exactly the budget
when it wants to be called again.

If a driver limits TX completion, it has to return budget as well when
the limit is hit, not the number of received packets.

Reported-and-tested-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: d75b1ade ("net: less interrupt masking in NAPI")
Cc: Manish Chopra <manish.chopra@qlogic.com>
Acked-by: Manish Chopra <manish.chopra@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>