The Engine.LinkChange method was recently removed in
e3df29d488f5ce50ee396b1f05a92e9cf1abb006 while misremembering how
Android's link state mechanism worked.
Rather than do some last minute rearchitecting of link state on
Android before Tailscale 1.6, restore the old Engine.LinkChange hook
for now so the Android client doesn't need any changes. But change how
it's implemented to instead inject an event into the link monitor.
Fixes#1427
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Don't use os.NewFile or (*os.File).Close on the AF_ROUTE socket. It
apparently does weird things to the fd and at least doesn't seem to
close it. Just use the unix package.
The test doesn't actually fail reliably before the fix, though. It
was an attempt. But this fixes the integration tests.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
