ci: extract enabling ipv6 on docker into a script

Author: pietroalbini

src/ci/azure-pipelines/steps/run.yml

@@ -111,15 +111,11 @@ steps:
   displayName: Install ninja
   condition: and(succeeded(), not(variables.SKIP_JOB))
 
-# Looks like docker containers have IPv6 disabled by default, so let's turn it
-# on since libstd tests require it
-- bash: |
-    set -e
-    sudo mkdir -p /etc/docker
-    echo '{"ipv6":true,"fixed-cidr-v6":"fd9a:8454:6789:13f7::/64"}' | sudo tee /etc/docker/daemon.json
-    sudo service docker restart
-  displayName: Enable IPv6
-  condition: and(succeeded(), not(variables.SKIP_JOB), eq(variables['Agent.OS'], 'Linux'))
+- bash: src/ci/scripts/enable-docker-ipv6.sh
+  env:
+    AGENT_OS: $(Agent.OS)
+  displayName: Enable IPv6 on Docker
+  condition: and(succeeded(), not(variables.SKIP_JOB))
 
 # Disable automatic line ending conversion (again). On Windows, when we're
 # installing dependencies, something switches the git configuration directory or

src/ci/scripts/enable-docker-ipv6.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+# Looks like docker containers have IPv6 disabled by default, so let's turn it
+# on since libstd tests require it
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if isLinux; then
+    sudo mkdir -p /etc/docker
+    echo '{"ipv6":true,"fixed-cidr-v6":"fd9a:8454:6789:13f7::/64"}' | sudo tee /etc/docker/daemon.json
+    sudo service docker restart
+fi