Standard IKEv2 X.509 exchange, but with pluto under callgrind

Callgrind accumulates an estimate of the on-CPU cost (~cpu-time) of
each function; not the off-CPU cost (for instance when a thread
becomes blocked).

There's a blog here: https://www.brendangregg.com/offcpuanalysis.html

Hence this is useful when investigating CPU bottle necks; but useless
when investigating stuck threads.

Set nhelpers=0 to stop threads becomming a distraction (pluto still
offloads crypto code, but as callbacks on the main thread's event
queue).
