lnwallet: increase legacy fee limit threshold to 1k sats

In this commit, we increase the legacy fee limit threshold (the amount
below which we'll allow 100% of funds to go to fees for the non-v2 RPC
calls) from 50 sats to 1k sats.

lnrpc/lightning.pb.go

@@ -1939,7 +1939,7 @@ type SendRequest struct {
 	//This value can be represented either as a percentage of the amount being
 	//sent, or as a fixed amount of the maximum fee the user is willing the pay to
 	//send the payment. If not specified, lnd will use a default value of 100%
-	//fees for small amounts (<=50 sat) or 5% fees for larger amounts.
+	//fees for small amounts (<=1k sat) or 5% fees for larger amounts.
 	FeeLimit *FeeLimit `protobuf:"bytes,8,opt,name=fee_limit,json=feeLimit,proto3" json:"fee_limit,omitempty"`
 	//
 	//The channel id of the channel that must be taken to the first hop. If zero,
@@ -8519,7 +8519,7 @@ type QueryRoutesRequest struct {
 	//This value can be represented either as a percentage of the amount being
 	//sent, or as a fixed amount of the maximum fee the user is willing the pay to
 	//send the payment. If not specified, lnd will use a default value of 100%
-	//fees for small amounts (<=50 sat) or 5% fees for larger amounts.
+	//fees for small amounts (<=1k sat) or 5% fees for larger amounts.
 	FeeLimit *FeeLimit `protobuf:"bytes,5,opt,name=fee_limit,json=feeLimit,proto3" json:"fee_limit,omitempty"`
 	//
 	//A list of nodes to ignore during path finding. When using REST, these fields

lnrpc/lightning.proto

@@ -754,7 +754,7 @@ message SendRequest {
     This value can be represented either as a percentage of the amount being
     sent, or as a fixed amount of the maximum fee the user is willing the pay to
     send the payment. If not specified, lnd will use a default value of 100%
-    fees for small amounts (<=50 sat) or 5% fees for larger amounts.
+    fees for small amounts (<=1k sat) or 5% fees for larger amounts.
     */
     FeeLimit fee_limit = 8;
 
@@ -2576,7 +2576,7 @@ message QueryRoutesRequest {
     This value can be represented either as a percentage of the amount being
     sent, or as a fixed amount of the maximum fee the user is willing the pay to
     send the payment. If not specified, lnd will use a default value of 100%
-    fees for small amounts (<=50 sat) or 5% fees for larger amounts.
+    fees for small amounts (<=1k sat) or 5% fees for larger amounts.
     */
     FeeLimit fee_limit = 5;
 

lnrpc/lightning.swagger.json

@@ -6238,7 +6238,7 @@
         },
         "fee_limit": {
           "$ref": "#/definitions/lnrpcFeeLimit",
-          "description": "The maximum number of satoshis that will be paid as a fee of the payment.\nThis value can be represented either as a percentage of the amount being\nsent, or as a fixed amount of the maximum fee the user is willing the pay to\nsend the payment. If not specified, lnd will use a default value of 100%\nfees for small amounts (\u003c=50 sat) or 5% fees for larger amounts."
+          "description": "The maximum number of satoshis that will be paid as a fee of the payment.\nThis value can be represented either as a percentage of the amount being\nsent, or as a fixed amount of the maximum fee the user is willing the pay to\nsend the payment. If not specified, lnd will use a default value of 100%\nfees for small amounts (\u003c=1k sat) or 5% fees for larger amounts."
         },
         "outgoing_chan_id": {
           "type": "string",