While debugging a failing test in airplane mode on macOS, I noticed
netcheck logspam about ICMP socket creation permission denied errors.
Apparently macOS just can't do those, or at least not in airplane
mode. Not worth spamming about.
Updates #cleanup
Change-Id: I302620cfd3c8eabb25202d7eef040c01bd8a843c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>