... in prep for merging the net/interfaces package into net/netmon.
This is a no-op change that updates a bunch of the API signatures ahead of
a future change to actually move things (and remove the type alias)
Updates tailscale/corp#10910
Updates tailscale/corp#18960
Updates #7967
Updates #3299
Change-Id: I477613388f09389214db0d77ccf24a65bff2199c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
