ifpps: Don't assume a maximum of 32 CPUs

There are people with machines containing far more than 32 CPUs. In
their case ifpps didn't work until now because of a limitation to 32
CPUs.

Rework ifpps to support an arbitrary number of CPUs. In order to still
remain within the display space, if more than 10 (TOP_CPUS) CPUs are
available, only the 10 top hitting (in terms of usr and sys time or irqs
respectively) are displayed.

Suggested-by: Daniel Borkmann <borkmann@iogearbox.net>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>