fix "host-gateway-ip" label not set for builder workers

Commit 21e50b89c92666589780eba6f83ad0851d8e9235 added a label on the buildkit
worker to advertise the host-gateway-ip. This option can be either set by the
user in the daemon config, or otherwise defaults to the gateway-ip.

If no value is set by the user, discovery of the gateway-ip happens when
initializing the network-controller (`NewDaemon`, `daemon.restore()`).

However d222bf097cd4c8121900c292f0f6ff243773c3c5 changed how we handle the
daemon config. As a result, the `cli.Config` used when initializing the
builder only holds configuration information form the daemon config
(user-specified or defaults), but is not updated with information set
by `NewDaemon`.

This patch adds an accessor on the daemon to get the current daemon config.
An alternative could be to return the config by `NewDaemon` (which should
likely be a _copy_ of the config).

Before this patch:

    docker buildx inspect default
    Name:   default
    Driver: docker

    Nodes:
    Name:      default
    Endpoint:  default
    Status:    running
    Buildkit:  v0.12.4+3b6880d2a00f
    Platforms: linux/arm64, linux/amd64, linux/amd64/v2, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
    Labels:
     org.mobyproject.buildkit.worker.moby.host-gateway-ip: <nil>

After this patch:

    docker buildx inspect default
    Name:   default
    Driver: docker

    Nodes:
    Name:      default
    Endpoint:  default
    Status:    running
    Buildkit:  v0.12.4+3b6880d2a00f
    Platforms: linux/arm64, linux/amd64, linux/amd64/v2, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
    Labels:
     org.mobyproject.buildkit.worker.moby.host-gateway-ip: 172.18.0.1

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 00c9785e2ef52ff96613f7ccc63c784ae6a7fc61)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/dockerd/daemon.go

@@ -301,7 +301,13 @@ func (cli *DaemonCli) start(opts *daemonOptions) (err error) {
 	routerCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 
-	routerOptions, err := newRouterOptions(routerCtx, cli.Config, d)
+	// Get a the current daemon config, because the daemon sets up config
+	// during initialization. We cannot user the cli.Config for that reason,
+	// as that only holds the config that was set by the user.
+	//
+	// FIXME(thaJeztah): better separate runtime and config data?
+	daemonCfg := d.Config()
+	routerOptions, err := newRouterOptions(routerCtx, &daemonCfg, d)
 	if err != nil {
 		return err
 	}

daemon/daemon.go

@@ -180,6 +180,11 @@ func (daemon *Daemon) config() *configStore {
 	return cfg
 }
 
+// Config returns daemon's config.
+func (daemon *Daemon) Config() config.Config {
+	return daemon.config().Config
+}
+
 // HasExperimental returns whether the experimental features of the daemon are enabled or not
 func (daemon *Daemon) HasExperimental() bool {
 	return daemon.config().Experimental