Kernel lockup with (debian) 4.16.0-2-rt-amd64

[Jason A. Donenfeld]

Hi Paul,

I got an -rt kernel up and running, enabled a bunch of nice debugging
options, and found a handful of problems, all of which were fixed by:
https://git.zx2c4.com/WireGuard/commit/?id=0f05452d043d8d047cf5d7987fc2732b97d676e6

I realize the solution in that patch is a bit of a bummer, but at the
very least it keeps things from breaking now. I'll see if I can
improve it somewhere down the line.

Jason