irqview: Fix some race conditions

Tested with:

while true ; do
	modprobe ixgbe
	ifup eth1
	ifup eth2
	for a in $(seq 200) ; do
		pethtool -i > /dev/null
	done
	rmmod ixgbe > /dev/null
done

That is a multi-q rx/tx adapter and thus uses lots of IRQs.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>