[PATCH v5 0/2 hurd] irqhelp + simplify ddekit

[Damien Zammit]

This adds an irqhelp library for simplified user irq registration.
The second patch implements the use case for ddekit (netdde).

TESTED: Copied 170000 files totalling 11GB inbound.
...
sent 10,932,485,258 bytes  received 3,563,749 bytes  1,473,960.38 bytes/sec
total size is 11,194,873,873  speedup is 1.02

Also tried ifdown and ifup a few times, works as before.

Thanks,
Damien