taprpc: update SendPayment docs

Author: GeorgeTsagk

taprpc/tapchannelrpc/tapchannel.pb.go

@@ -124,8 +124,8 @@ message SendPaymentRequest {
     uint64 asset_amount = 2;
 
     // The node identity public key of the peer to ask for a quote for sending
-    // out the assets and converting them to satoshis. This must be specified if
-    // there are multiple channels with the given asset ID.
+    // out the assets and converting them to satoshis. If set, only a quote with
+    // this peer may be negotiated to carry out the payment.
     bytes peer_pubkey = 3;
 
     // The full lnd payment request to send. All fields behave the same way as

taprpc/tapchannelrpc/tapchannel.proto

@@ -1691,7 +1691,7 @@
         "peer_pubkey": {
           "type": "string",
           "format": "byte",
-          "description": "The node identity public key of the peer to ask for a quote for sending\nout the assets and converting them to satoshis. This must be specified if\nthere are multiple channels with the given asset ID."
+          "description": "The node identity public key of the peer to ask for a quote for sending\nout the assets and converting them to satoshis. If set, only a quote with\nthis peer may be negotiated to carry out the payment."
         },
         "payment_request": {
           "$ref": "#/definitions/routerrpcSendPaymentRequest",