Improve checking dummy kernel module

Signed-off-by: Stefan Scherer <scherer_stefan@icloud.com>

Makefile

@@ -84,16 +84,6 @@ binary: build
 	$(DOCKER_RUN_DOCKER) hack/make.sh binary
 
 build: bundles
-ifeq ($(DOCKER_OSARCH), linux/arm)
-	# A few libnetwork integration tests require that the kernel be
-	# configured with "dummy" network interface and has the module
-	# loaded. However, the dummy module is not available by default
-	# on arm images. This ensures that it's built and loaded.
-	echo "Syncing kernel modules"
-	oc-sync-kernel-modules
-	depmod
-	modprobe dummy
-endif
 	docker build ${DOCKER_BUILD_ARGS} -t "$(DOCKER_IMAGE)" -f "$(DOCKERFILE)" .
 
 bundles:

project/ARM.md

@@ -28,3 +28,18 @@ So for example in order to build a Docker binary one has to
 1. clone the Docker/Docker repository on an ARM device `git clone git@github.com:docker/docker.git`  
 2. change into the checked out repository with `cd docker`  
 3. execute `make binary` to create a Docker Engine binary for ARM  
+
+## Kernel modules
+A few libnetwork integration tests require that the kernel be
+configured with "dummy" network interface and has the module
+loaded. However, the dummy module may be not loaded automatically.
+
+To load the kernel module permanently, run these commands as `root`.
+
+    modprobe dummy
+    echo "dummy" >> /etc/modules
+
+On some systems you also have to sync your kernel modules.
+
+    oc-sync-kernel-modules
+    depmod