wgengine/netstack: add missing error logging in a RST case

Updates #2642

Change-Id: I9f2f8fd28fc980208b0739eb9caf9db7b0977c09
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