[WireGuard] Error building against grsec-enabled kernel

[Jason A. Donenfeld]

Hi,

I've switched to using the same strategy of tun.c, and simply
resetting all the fields, even if this is semantically incorrect, as
the rest of the kernel seems to do this in fact:
https://git.zx2c4.com/WireGuard/commit/?id=95a869e45905766878cc4fee1a27a1c933786361

This should make WireGuard run fine on PaX. That, combined with the
previous PaX-motivated commit, should make WireGuard work with
Grsecurity kernels without any modification necessary. This work will
be part of the next snapshot I tag.

Jason