ifpps: beautify output with > 10 cpus

I've tested it on a 24 CPU machine, and it does not look so nice if
there's different padding along the lines. This patch fixes it.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
ifpps: fix bug_on trigger when parsing irq number

When parsing irq numbers on e.g. 24 CPU machines, procfs lines can get
very long, so our static temporary buffer size will fail here with:

  Assertion `!(stats->irq_nr == 0)' failed.

So allocate it relative to the CPU number.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
man: ifpps: document ifpps behaviour when CPU > 10

Document the behaviour of ifpps when we switch to heavy hitter mode.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
ifpps: minor: minor output formatting adaption

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
ifpps: Use strtoul() to convert unsigned value

The refresh interval can only be positive and is stored in an uint64_t,
so use strtoul() to convert it.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>