irq mode can be used to show how a core is interrupted by other tasks.
This mode does not handle packets. It only loops reading tsc.
When the difference between two consecutive calls to rdtsc() is high
then it means the core was interrupted.
This task implementes the display, so that we can see a histogram of
interrupts as well as the maximum, per core.
Command line is also supported, through "show irq buckets" (too show
the intervals of each buckets, in micrcoseconds), and the stats
command line (showing the number of items in each buckets and the max)..
Signed-off-by: Xavier Simonart <email@example.com>