lnrpc+rpcserver: add payment_addr field to PayReq

lnrpc/rpc.proto

@@ -2615,6 +2615,7 @@ message PayReq {
     string fallback_addr = 8 [json_name = "fallback_addr"];
     int64 cltv_expiry = 9 [json_name = "cltv_expiry"];
     repeated RouteHint route_hints = 10 [json_name = "route_hints"];
+    bytes payment_addr = 11 [json_name = "payment_addr"];
 }
 
 message FeeReportRequest {}

lnrpc/rpc.swagger.json

@@ -3248,6 +3248,10 @@
           "items": {
             "$ref": "#/definitions/lnrpcRouteHint"
           }
+        },
+        "payment_addr": {
+          "type": "string",
+          "format": "byte"
         }
       }
     },

rpcserver.go

@@ -4593,6 +4593,12 @@ func (r *rpcServer) DecodePayReq(ctx context.Context,
 		amt = int64(payReq.MilliSat.ToSatoshis())
 	}
 
+	// Extract the payment address from the payment request, if present.
+	var paymentAddr []byte
+	if payReq.PaymentAddr != nil {
+		paymentAddr = payReq.PaymentAddr[:]
+	}
+
 	dest := payReq.Destination.SerializeCompressed()
 	return &lnrpc.PayReq{
 		Destination:     hex.EncodeToString(dest),
@@ -4605,6 +4611,7 @@ func (r *rpcServer) DecodePayReq(ctx context.Context,
 		Expiry:          expiry,
 		CltvExpiry:      int64(payReq.MinFinalCLTVExpiry()),
 		RouteHints:      routeHints,
+		PaymentAddr:     paymentAddr,
 	}, nil
 }