ipn,tailcfg: add VIPService struct and c2n to fetch them from client (#14046)

* ipn,tailcfg: add VIPService struct and c2n to fetch them from client

Updates tailscale/corp#22743, tailscale/corp#22955

Signed-off-by: Naman Sood <mail@nsood.in>

* more review fixes

Signed-off-by: Naman Sood <mail@nsood.in>

* don't mention PeerCapabilityServicesDestination since it's currently unused

Signed-off-by: Naman Sood <mail@nsood.in>

---------

Signed-off-by: Naman Sood <mail@nsood.in>

tailcfg/tailcfg_test.go

@@ -66,6 +66,7 @@ func TestHostinfoEqual(t *testing.T) {
 		"Userspace",
 		"UserspaceRouter",
 		"AppConnector",
+		"ServicesHash",
 		"Location",
 	}
 	if have := fieldsOf(reflect.TypeFor[Hostinfo]()); !reflect.DeepEqual(have, hiHandles) {
@@ -240,6 +241,16 @@ func TestHostinfoEqual(t *testing.T) {
 			&Hostinfo{AppConnector: opt.Bool("false")},
 			false,
 		},
+		{
+			&Hostinfo{ServicesHash: "73475cb40a568e8da8a045ced110137e159f890ac4da883b6b17dc651b3a8049"},
+			&Hostinfo{ServicesHash: "73475cb40a568e8da8a045ced110137e159f890ac4da883b6b17dc651b3a8049"},
+			true,
+		},
+		{
+			&Hostinfo{ServicesHash: "084c799cd551dd1d8d5c5f9a5d593b2e931f5e36122ee5c793c1d08a19839cc0"},
+			&Hostinfo{},
+			false,
+		},
 	}
 	for i, tt := range tests {
 		got := tt.a.Equal(tt.b)