tailcfg: add Node.SelfNodeV4MasqAddrForThisPeer

This only adds the field, to be used in a future commit.

Updates tailscale/corp#8020

Co-authored-by: Melanie Warrick <warrick@tailscale.com>
Signed-off-by: Maisem Ali <maisem@tailscale.com>

tailcfg/tailcfg_test.go

@@ -349,7 +349,7 @@ func TestNodeEqual(t *testing.T) {
 		"Capabilities",
 		"UnsignedPeerAPIOnly",
 		"ComputedName", "computedHostIfDifferent", "ComputedNameWithHost",
-		"DataPlaneAuditLogID", "Expired",
+		"DataPlaneAuditLogID", "Expired", "SelfNodeV4MasqAddrForThisPeer",
 	}
 	if have := fieldsOf(reflect.TypeOf(Node{})); !reflect.DeepEqual(have, nodeHandles) {
 		t.Errorf("Node.Equal check might be out of sync\nfields: %q\nhandled: %q\n",
@@ -534,6 +534,16 @@ func TestNodeEqual(t *testing.T) {
 			&Node{},
 			false,
 		},
+		{
+			&Node{},
+			&Node{SelfNodeV4MasqAddrForThisPeer: netip.MustParseAddr("100.64.0.1")},
+			false,
+		},
+		{
+			&Node{SelfNodeV4MasqAddrForThisPeer: netip.MustParseAddr("100.64.0.1")},
+			&Node{SelfNodeV4MasqAddrForThisPeer: netip.MustParseAddr("100.64.0.1")},
+			true,
+		},
 	}
 	for i, tt := range tests {
 		got := tt.a.Equal(tt.b)