tailcfg: make SelfNodeV4MasqAddrForThisPeer a pointer

This makes `omitempty` actually work, and saves bytes in each map response.

Updates tailscale/corp#8020

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/magicsock/magicsock_test.go

@@ -50,6 +50,7 @@ import (
 	"tailscale.com/types/netlogtype"
 	"tailscale.com/types/netmap"
 	"tailscale.com/types/nettype"
+	"tailscale.com/types/ptr"
 	"tailscale.com/util/cibuild"
 	"tailscale.com/util/racebuild"
 	"tailscale.com/wgengine/filter"
@@ -2240,7 +2241,7 @@ func TestIsWireGuardOnlyPeerWithMasquerade(t *testing.T) {
 				IsWireGuardOnly:               true,
 				Addresses:                     []netip.Prefix{wgaip},
 				AllowedIPs:                    []netip.Prefix{wgaip},
-				SelfNodeV4MasqAddrForThisPeer: masqip.Addr(),
+				SelfNodeV4MasqAddrForThisPeer: ptr.To(masqip.Addr()),
 			},
 		},
 	}

wgengine/wgcfg/config.go

@@ -37,7 +37,7 @@ type Peer struct {
 	PublicKey           key.NodePublic
 	DiscoKey            key.DiscoPublic // present only so we can handle restarts within wgengine, not passed to WireGuard
 	AllowedIPs          []netip.Prefix
-	V4MasqAddr          netip.Addr // if non-zero, masquerade IPv4 traffic to this peer using this address
+	V4MasqAddr          *netip.Addr // if non-nil, masquerade IPv4 traffic to this peer using this address
 	PersistentKeepalive uint16
 	// wireguard-go's endpoint for this peer. It should always equal Peer.PublicKey.
 	// We represent it explicitly so that we can detect if they diverge and recover.

wgengine/wgcfg/wgcfg_clone.go

@@ -54,6 +54,10 @@ func (src *Peer) Clone() *Peer {
 	dst := new(Peer)
 	*dst = *src
 	dst.AllowedIPs = append(src.AllowedIPs[:0:0], src.AllowedIPs...)
+	if dst.V4MasqAddr != nil {
+		dst.V4MasqAddr = new(netip.Addr)
+		*dst.V4MasqAddr = *src.V4MasqAddr
+	}
 	return dst
 }
 
@@ -62,7 +66,7 @@ var _PeerCloneNeedsRegeneration = Peer(struct {
 	PublicKey           key.NodePublic
 	DiscoKey            key.DiscoPublic
 	AllowedIPs          []netip.Prefix
-	V4MasqAddr          netip.Addr
+	V4MasqAddr          *netip.Addr
 	PersistentKeepalive uint16
 	WGEndpoint          key.NodePublic
 }{})