env/linux-x86-buster, dashboard: add netbase package to the host

This change adds the netbase package to the host. The netbase package
includes several components necessary for TCP/IP based networking.
Network related unit tests were failing on builders using this host
without this package.

Fixes golang/go#42750

Change-Id: Id98d46efac4fe98ecf475035218be181c3d8dec0
Reviewed-on: https://go-review.googlesource.com/c/build/+/272486
Trust: Carlos Amedee <[email protected]>
Run-TryBot: Carlos Amedee <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: cagedmantis

dashboard/builders.go

@@ -1789,7 +1789,6 @@ func init() {
 		env: []string{
 			"GO_DISABLE_OUTBOUND_NETWORK=1",
 		},
-		KnownIssue: 42750,
 	})
 	addBuilder(BuildConfig{
 		Name:     "linux-amd64-longtest",

env/linux-x86-buster/Dockerfile

@@ -16,9 +16,11 @@ ENV DEBIAN_FRONTEND noninteractive
 # libc6-dev-i386 gcc-multilib: for 32-bit builds
 # procps lsof psmisc: misc basic tools
 # libgles2-mesa-dev libopenal-dev fonts-droid-fallback: required by x/mobile repo
+# netbase: for net package tests, issue 42750
 RUN apt-get update && apt-get install -y \
 	--no-install-recommends \
 	ca-certificates \
+	netbase \
 	curl \
 	gdb \
 	strace \