portlist: use win32 calls instead of running netstat process [windows]

Turns out using win32 instead of shelling out to child processes is a
bit faster:

    name                  old time/op    new time/op    delta
    GetListIncremental-4     278ms ± 2%       0ms ± 7%  -99.93%  (p=0.000 n=8+10)

    name                  old alloc/op   new alloc/op   delta
    GetListIncremental-4     238kB ± 0%       9kB ± 0%  -96.12%  (p=0.000 n=10+8)

    name                  old allocs/op  new allocs/op  delta
    GetListIncremental-4     1.19k ± 0%     0.02k ± 0%  -98.49%  (p=0.000 n=10+10)

Fixes #3876 (sadly)

Change-Id: I1195ac5de21a8a8b3cdace5871d263e81aa27e91
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f