htlcswitch: pass quit chans as unidirectional

This is a requirement for replacing the quit channel with a Context.
The Done() channel of a Context is always recv-only, so all users of
that channel must not expect a bidirectional channel.

htlcswitch/mailbox_test.go

@@ -250,7 +250,7 @@ func newMailboxContext(t *testing.T, startTime time.Time,
 	return ctx
 }
 
-func (c *mailboxContext) forward(_ chan struct{},
+func (c *mailboxContext) forward(_ <-chan struct{},
 	pkts ...*htlcPacket) error {
 
 	for _, pkt := range pkts {
@@ -706,7 +706,7 @@ func TestMailOrchestrator(t *testing.T) {
 	// First, we'll create a new instance of our orchestrator.
 	mo := newMailOrchestrator(&mailOrchConfig{
 		failMailboxUpdate: failMailboxUpdate,
-		forwardPackets: func(_ chan struct{},
+		forwardPackets: func(_ <-chan struct{},
 			pkts ...*htlcPacket) error {
 
 			return nil