rpc: add ban_duration field to listbanned

src/rpc/net.cpp

@@ -752,6 +752,7 @@ static RPCHelpMan listbanned()
                         {RPCResult::Type::STR, "address", "The IP/Subnet of the banned node"},
                         {RPCResult::Type::NUM_TIME, "ban_created", "The " + UNIX_EPOCH_TIME + " the ban was created"},
                         {RPCResult::Type::NUM_TIME, "banned_until", "The " + UNIX_EPOCH_TIME + " the ban expires"},
+                        {RPCResult::Type::NUM_TIME, "ban_duration", "The ban duration, in seconds"},
                     }},
             }},
                 RPCExamples{
@@ -776,6 +777,7 @@ static RPCHelpMan listbanned()
         rec.pushKV("address", entry.first.ToString());
         rec.pushKV("ban_created", banEntry.nCreateTime);
         rec.pushKV("banned_until", banEntry.nBanUntil);
+        rec.pushKV("ban_duration", (banEntry.nBanUntil - banEntry.nCreateTime));
 
         bannedAddresses.push_back(rec);
     }