invoices: return accept height in hodl event

This is a preparation for passing back the accept height in the
incorrect payment details failure message to the sender.

channeldb/invoices.go

@@ -272,7 +272,7 @@ type InvoiceHTLC struct {
 
 	// State indicates the state the invoice htlc is currently in. A
 	// cancelled htlc isn't just removed from the invoice htlcs map, because
-	// we need AcceptedHeight to properly cancel the htlc back.
+	// we need AcceptHeight to properly cancel the htlc back.
 	State HtlcState
 }