net/netcheck: clean up ICMP probe AddrPort lookup

Fixes #14200

Change-Id: Ib086814cf63dda5de021403fe1db4fb2a798eaae
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