Report minfeefilter value in getpeerinfo rpc

Lowering the minimum relay fee is only useful when many nodes in the
p2p network also lower the fee, so to make it easier to understand
progress on that front, this includes the value of the minfeefilter in
getpeerinfo, so you at least have visibility to what fees your neighbours
are currently accepting.

src/rpc/net.cpp

@@ -102,6 +102,7 @@ static UniValue getpeerinfo(const JSONRPCRequest& request)
             "       ...\n"
             "    ],\n"
             "    \"whitelisted\": true|false, (boolean) Whether the peer is whitelisted\n"
+            "    \"minfeefilter\": n,         (numeric) The minimum fee rate for transactions this peer accepts\n"
             "    \"bytessent_per_msg\": {\n"
             "       \"addr\": n,              (numeric) The total bytes sent aggregated by message type\n"
             "       ...\n"
@@ -169,6 +170,7 @@ static UniValue getpeerinfo(const JSONRPCRequest& request)
             obj.pushKV("inflight", heights);
         }
         obj.pushKV("whitelisted", stats.fWhitelisted);
+        obj.pushKV("minfeefilter", ValueFromAmount(stats.minFeeFilter));
 
         UniValue sendPerMsgCmd(UniValue::VOBJ);
         for (const mapMsgCmdSize::value_type &i : stats.mapSendBytesPerMsgCmd) {