Don't do anything with UPnP, NAT-PMP, PCP yet, but see how common they are in the wild. Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
For discovering where we might direct NAT-PMP/PCP/UPnP queries at in the future.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Basically, don't trust the OS-level link monitor to only tell you interesting things. Sanity check it. Also, move the interfaces package into the net directory now that we have it.