net: correct TestIPConnSpecificMethods comment after CL 476217

net: correct TestIPConnSpecificMethods comment after CL 476217

As suggested by Cherry in
https://go-review.googlesource.com/c/go/+/476217/5/src/net/protoconn_test.go#171

Change-Id: I4ce3c034b44953720c543a87639fd173f86af7dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/476535
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>