Wireguard status

With the below three changes, wireguard (via wireguard-go) works on
dfly. (Tested with "wg-quick up ./wg0.conf" with a simple configuration
file.)

Eventually #1 and #2 should be upstreamed (nothing to upstream for #3).
If people are impatient, I'm happy to try putting some patches in
dports to get it available sooner.

1. Aaron Li's wireguard-go patch from last year, plus a couple of
   small tweaks.

   See https://github.com/falsifian/wireguard-go/commit/56398eaffb35f4ab62ed025026c25ffcf96d3376 plus the two preceding patches.

   I haven't sent it upstream yet. I'm wondering what the best way to
   present the combined changes is.

2. The x/net go library needs one more patch to get interface info with
   dfly's RTM_VERSION 7. Fixed by
   https://go-review.googlesource.com/c/net/+/328331/ which is under
   review.

3. net/wireguard needs a small tweak to work with the latest wireguard-go:

   https://git.zx2c4.com/wireguard-tools/commit/?id=457f96b65e4f7241aceaa7cb9c7bbce7be1a2212

   Probably the port just be updated, but I haven't tried that.

-- 
James