tailcfg: add missing Node.DERP check in Node.Equals

Updates tailscale/corp#549

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
(cherry picked from commit 1f7a7a4ffe)

tailcfg/tailcfg.go

@@ -613,6 +613,7 @@ func (n *Node) Equal(n2 *Node) bool {
 		eqCIDRs(n.Addresses, n2.Addresses) &&
 		eqCIDRs(n.AllowedIPs, n2.AllowedIPs) &&
 		eqStrings(n.Endpoints, n2.Endpoints) &&
+		n.DERP == n2.DERP &&
 		n.Hostinfo.Equal(&n2.Hostinfo) &&
 		n.Created.Equal(n2.Created) &&
 		eqTimePtr(n.LastSeen, n2.LastSeen) &&

tailcfg/tailcfg_test.go

@@ -315,6 +315,11 @@ func TestNodeEqual(t *testing.T) {
 			&Node{LastSeen: &now},
 			true,
 		},
+		{
+			&Node{DERP: "foo"},
+			&Node{DERP: "bar"},
+			false,
+		},
 	}
 	for i, tt := range tests {
 		got := tt.a.Equal(tt.b)