daemon: add ULA prefix by default

So far, Moby only had IPv4 prefixes in its 'default-address-pools'. To
get dynamic IPv6 subnet allocations, users had to redefine this
parameter to include IPv6 base network(s). This is needlessly complex
and against Moby's 'batteries-included' principle.

This change generates a ULA base network by deriving a ULA Global ID
from the Engine's Host ID and put that base network into
'default-address-pools'. This Host ID is stable over time (except if
users remove their '/var/lib/docker/engine-id') and thus the GID is
stable too.

This ULA base network won't be put into 'default-address-pools' if users
have manually configured it.

This is loosely based on https://datatracker.ietf.org/doc/html/rfc4193#section-3.2.2.

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

daemon/daemon_test.go

@@ -1,6 +1,7 @@
 package daemon // import "github.com/docker/docker/daemon"
 
 import (
+	"net/netip"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -313,3 +314,30 @@ func TestFindNetworkErrorType(t *testing.T) {
 		t.Error("The FindNetwork method MUST always return an error that implements the NotFound interface and is ErrNoSuchNetwork")
 	}
 }
+
+// TestDeriveULABaseNetwork checks that for a given hostID, the derived prefix is stable over time.
+func TestDeriveULABaseNetwork(t *testing.T) {
+	testcases := []struct {
+		name      string
+		hostID    string
+		expPrefix netip.Prefix
+	}{
+		{
+			name:      "Empty hostID",
+			expPrefix: netip.MustParsePrefix("fd42:98fc:1c14::/48"),
+		},
+		{
+			name:      "499d4bc0-b0b3-416f-b1ee-cf6486315593",
+			hostID:    "499d4bc0-b0b3-416f-b1ee-cf6486315593",
+			expPrefix: netip.MustParsePrefix("fd62:fb69:18af::/48"),
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			nw := deriveULABaseNetwork(tc.hostID)
+			assert.Equal(t, nw.Base, tc.expPrefix)
+			assert.Equal(t, nw.Size, 64)
+		})
+	}
+}