net/sockstats: quiet some log spam in release builds

Updates #13731

Change-Id: Ibee85426827ebb9e43a1c42a9c07c847daa50117
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f