Now cmd/derper doesn't depend on iptables, nftables, and netlink code :)
But this is really just a cleanup step I noticed on the way to making
tsnet applications able to not link all the OS router code which they
don't use.
Updates #17313
Change-Id: Ic7b4e04e3a9639fd198e9dbeb0f7bae22a4a47a9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
