routerrpc: update QueryProbability documentation

Changes the docstring of QueryProbability to reflect changes that were
introduced in lightningnetwork#6857.

Author: bitromortac

lnrpc/routerrpc/router.proto

@@ -95,7 +95,9 @@ service Router {
 
     /*
     Deprecated. QueryProbability returns the current success probability
-    estimate for a given node pair and amount.
+    estimate for a given node pair and amount. The call returns a zero success
+    probability if no channel is available or if the amount violates min/max
+    HTLC constraints.
     */
     rpc QueryProbability (QueryProbabilityRequest)
         returns (QueryProbabilityResponse);

lnrpc/routerrpc/router.swagger.json

@@ -116,7 +116,7 @@
     },
     "/v2/router/mc/probability/{from_node}/{to_node}/{amt_msat}": {
       "get": {
-        "summary": "Deprecated. QueryProbability returns the current success probability\nestimate for a given node pair and amount.",
+        "summary": "Deprecated. QueryProbability returns the current success probability\nestimate for a given node pair and amount. The call returns a zero success\nprobability if no channel is available or if the amount violates min/max\nHTLC constraints.",
         "operationId": "Router_QueryProbability",
         "responses": {
           "200": {