net: stop using GetHostByName and GetServByName

net: stop using GetHostByName and GetServByName

Go 1.6 requires Windows XP or later. I have:

C:\>systeminfo | findstr /B /C:"OS Name" /C:"OS Version"
OS Name:                   Microsoft Windows XP Professional
OS Version:                5.1.2600 Service Pack 3 Build 2600

Running "go test" PASSes on my system after this CL is applied.

Change-Id: Id59d169138c4a4183322c89ee7e766fb74d381fa
Reviewed-on: https://go-review.googlesource.com/22209
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>