Addr's MarshalBinary required two allocations in the case of a zone
existing, and AddrPort and Prefix both required three. This refactors
things slightly so that each marshal function only needs a single
allocation.
Change-Id: I9bde9969fedc1cad64bebb607188c4287f6a0d01
Reviewed-on: https://go-review.googlesource.com/c/go/+/361054
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>