add network read performance collection support. (#8038)

ReST API on /minio/admin/v1/performance?perfType=net[?size=N] 
returns

```
{
  "PEER-1": [
             {
	       "addr": ADDR,
	       "readPerf": DURATION,
	       "error": ERROR,
	     },
	     ...
	   ],
  ...
  ...
  "PEER-N": [
             {
	       "addr": ADDR,
	       "readPerf": DURATION,
	       "error": ERROR,
	     },
	     ...
	   ]
}
```

cmd/notification.go

@@ -907,6 +907,55 @@ func (sys *NotificationSys) Send(args eventArgs) []event.TargetIDErr {
 	return sys.send(args.BucketName, args.ToEvent(), targetIDs...)
 }
 
+// NetReadPerfInfo - Network read performance information.
+func (sys *NotificationSys) NetReadPerfInfo(size int64) []ServerNetReadPerfInfo {
+	reply := make([]ServerNetReadPerfInfo, len(sys.peerClients))
+
+	// Execution is done serially.
+	for i, client := range sys.peerClients {
+		if client == nil {
+			continue
+		}
+
+		info, err := client.NetReadPerfInfo(size)
+		if err != nil {
+			reqInfo := (&logger.ReqInfo{}).AppendTags("remotePeer", client.host.String())
+			ctx := logger.SetReqInfo(context.Background(), reqInfo)
+			logger.LogIf(ctx, err)
+
+			info.Addr = client.host.String()
+			info.Error = err.Error()
+		}
+
+		reply[i] = info
+	}
+
+	return reply
+}
+
+// CollectNetPerfInfo - Collect network performance information of all peers.
+func (sys *NotificationSys) CollectNetPerfInfo(size int64) map[string][]ServerNetReadPerfInfo {
+	reply := map[string][]ServerNetReadPerfInfo{}
+
+	// Execution is done serially.
+	for _, client := range sys.peerClients {
+		if client == nil {
+			continue
+		}
+
+		info, err := client.CollectNetPerfInfo(size)
+		if err != nil {
+			reqInfo := (&logger.ReqInfo{}).AppendTags("remotePeer", client.host.String())
+			ctx := logger.SetReqInfo(context.Background(), reqInfo)
+			logger.LogIf(ctx, err)
+		}
+
+		reply[client.host.String()] = info
+	}
+
+	return reply
+}
+
 // DrivePerfInfo - Drive speed (read and write) information
 func (sys *NotificationSys) DrivePerfInfo() []ServerDrivesPerfInfo {
 	reply := make([]ServerDrivesPerfInfo, len(sys.peerClients))