Install and run firewalld for CI's firewalld tests

The github action running bake expected FIREWALLD to be set, but
DOCKER_FIREWALLD was set instead, so firewalld wasn't installed
in the dev image.

The dind-systemd script expected DOCKER_FIREWALLD to be set if it
needed to run firewalld, and it was. But it had no effect.

In CI, bake builds the image then make runs it - and the use the
same env. So, align on FIREWALLD (as it's not a docker feature).

Signed-off-by: Rob Murray <rob.murray@docker.com>

Makefile

@@ -38,7 +38,6 @@ DOCKER_ENVS := \
 	-e DOCKERCLI_INTEGRATION_REPOSITORY \
 	-e DOCKER_DEBUG \
 	-e DOCKER_EXPERIMENTAL \
-	-e DOCKER_FIREWALLD \
 	-e DOCKER_GITCOMMIT \
 	-e DOCKER_GRAPHDRIVER \
 	-e DOCKER_LDFLAGS \
@@ -50,6 +49,7 @@ DOCKER_ENVS := \
 	-e DOCKER_USERLANDPROXY \
 	-e DOCKERD_ARGS \
 	-e DELVE_PORT \
+	-e FIREWALLD \
 	-e GITHUB_ACTIONS \
 	-e TEST_FORCE_VALIDATE \
 	-e TEST_INTEGRATION_DIR \
@@ -150,7 +150,7 @@ DOCKER_BUILD_ARGS += --build-arg=DOCKERCLI_INTEGRATION_REPOSITORY
 ifdef DOCKER_SYSTEMD
 DOCKER_BUILD_ARGS += --build-arg=SYSTEMD=true
 endif
-ifdef DOCKER_FIREWALLD
+ifdef FIREWALLD
 DOCKER_BUILD_ARGS += --build-arg=FIREWALLD=true
 endif