lrdp_v2 : Fix for broken irqstat.py for kernel 3.18

Fix for broken irqstat.py for 3.18 kernel.
In kernel 3.18, affinity is part of struct irq_data
whereas in kernel >= 4.4 affinity is part fo struct irq_common_data

Change-Id: I6c5b5417df86a818c1fc362ab881057074521d2f