env/linux-arm64: add netbase for the /etc/services file

The /etc/services file used to be elsewhere in Jessie. When we
upgraded to Buster we lost it and now need the netbase package.
We've had to do this for other builders we upgraded from Jessie but
I forgot.

Updates golang/go#34905

Change-Id: I24c4271839cc2c4a9556f88d7347b031bd3a29bb
Reviewed-on: https://go-review.googlesource.com/c/build/+/201459
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

env/linux-arm64/Dockerfile

@@ -8,9 +8,10 @@ ENV DEBIAN_FRONTEND noninteractive
 
 RUN apt-get update && \
     apt-get install --yes \
-          curl gcc strace ca-certificates \
-          procps lsof psmisc
-RUN apt-get install --yes --no-install-recommends openssh-server
+          gcc curl strace \
+          ca-certificates netbase \
+          procps lsof psmisc \
+          openssh-server
 
 RUN mkdir /usr/local/go-bootstrap && \
     curl --silent https://storage.googleapis.com/go-builder-data/gobootstrap-linux-arm64.tar.gz | \