net: pass around pointers to SockaddrInetN

net: pass around pointers to SockaddrInetN

...instead of the structs themselves.
Escape analysis can handle this,
and it'll avoid a bunch of large struct copies.

Change-Id: Ia9c6064ed32a4c26d5a96dae2ed7d7ece6d38704
Reviewed-on: https://go-review.googlesource.com/c/go/+/361264
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>