Add support for wireguard peer descriptions

"wgdescr[iption] foo" to label one peer (amongst many) on a wg(4) interface,
"-wgdescr[iption]" or "wgdescr ''" to remove the label, completely analogous
to existing interface discriptions.

Idea/initial diff from Mikolaj Kucharski (OK sthen)
Tests/prodded by Hrvoje Popovski
Tweaks/manual bits from me
Feedback deraadt sthen mvs claudio
OK claudio

add missing rcs id

add wg(4), an in kernel driver for WireGuard vpn communication.

thanks to Matt Dunwoodie and Jason A. Donenfeld for their effort.
it's at least as functional as the go implementation, and maybe
more so since this one works on more architectures.

i'm sure there's further development that can be done, but you can
say that about anything and everything that's in the tree.

ok deraadt@

back out, this isn't part of a vlan change.

get rid of ifv_linkmib and a bunch of useless macros

add missing rcs id

add wg(4), an in kernel driver for WireGuard vpn communication.

thanks to Matt Dunwoodie and Jason A. Donenfeld for their effort.
it's at least as functional as the go implementation, and maybe
more so since this one works on more architectures.

i'm sure there's further development that can be done, but you can
say that about anything and everything that's in the tree.

ok deraadt@

back out, this isn't part of a vlan change.

get rid of ifv_linkmib and a bunch of useless macros