lnrpc+rpcserver: add remote reserve to openchannel request

lnrpc/lightning.proto

@@ -2217,6 +2217,13 @@ message OpenChannelRequest {
     to use the default fee rate value specified in the config or 0.
     */
     bool use_fee_rate = 24;
+
+    /*
+    The number of satoshis we require the remote peer to reserve. This value,
+    if specified, must be above the dust limit and below 20% of the channel
+    capacity.
+    */
+    uint64 remote_chan_reserve_sat = 25;
 }
 message OpenStatusUpdate {
     oneof update {

lnrpc/lightning.swagger.json

@@ -5679,6 +5679,11 @@
         "use_fee_rate": {
           "type": "boolean",
           "description": "If use_fee_rate is true the open channel announcement will update the\nchannel fee rate with the value specified in fee_rate. In the case of\na fee_rate of 0 use_fee_rate is needed downstream to distinguish whether\nto use the default fee rate value specified in the config or 0."
+        },
+        "remote_chan_reserve_sat": {
+          "type": "string",
+          "format": "uint64",
+          "description": "The number of satoshis we require the remote peer to reserve. This value,\nif specified, must be above the dust limit and below 20% of the channel\ncapacity."
         }
       }
     },

rpcserver.go

@@ -1910,6 +1910,7 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 	remoteCsvDelay := uint16(in.RemoteCsvDelay)
 	maxValue := lnwire.MilliSatoshi(in.RemoteMaxValueInFlightMsat)
 	maxHtlcs := uint16(in.RemoteMaxHtlcs)
+	remoteChanReserve := btcutil.Amount(in.RemoteChanReserveSat)
 
 	globalFeatureSet := r.server.featureMgr.Get(feature.SetNodeAnn)
 
@@ -1937,6 +1938,13 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 		channelFeeRate = &in.FeeRate
 	}
 
+	// Ensure that the remote channel reserve does not exceed 20% of the
+	// channel capacity.
+	if remoteChanReserve >= localFundingAmt/5 {
+		return nil, fmt.Errorf("remote channel reserve must be less " +
+			"than the %%20 of the channel capacity")
+	}
+
 	// Ensure that the user doesn't exceed the current soft-limit for
 	// channel size. If the funding amount is above the soft-limit, then
 	// we'll reject the request.
@@ -2102,6 +2110,7 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 		FundingFeePerKw:   feeRate,
 		Private:           in.Private,
 		RemoteCsvDelay:    remoteCsvDelay,
+		RemoteChanReserve: remoteChanReserve,
 		MinConfs:          minConfs,
 		ShutdownScript:    script,
 		MaxValueInFlight:  maxValue,