Its doc said its signature matched a std signature, but it used
Tailscale-specific types.
Nowadays it's the caller (func control) that curries the logf/netmon
and returns the std-matching signature.
Updates #cleanup (while answering a question on Slack)
Change-Id: Ic99de41fc6a1c720575a7f33c564d0bcfd9a2c30
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>