Reduce to just a single external endpoint.
Convert from a variadic number of interfaces to a slice there.
name old time/op new time/op delta
Hash-8 14.4µs ± 0% 14.0µs ± 1% -3.08% (p=0.000 n=9+9)
name old alloc/op new alloc/op delta
Hash-8 873B ± 0% 793B ± 0% -9.16% (p=0.000 n=9+6)
name old allocs/op new allocs/op delta
Hash-8 18.0 ± 0% 14.0 ± 0% -22.22% (p=0.000 n=10+10)
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>