Fail to send alert messages via mail with tls enabled on a port other than 465

[xiaosuiba]

What happened:
Fail to send alert messages via mail with tls enabled on a port other than 465.

What you expected to happen:
Could send alert messages via mail with tls enabled on any port specified.

How to reproduce it (as minimally and precisely as possible):

1. Create a channel as the picture shown above.
2. Create an alarmpolicy and use the channel created.
3. Trigger an alarm.

Anything else we need to know?:
pkg/notify/controller/messagerequest/smtp/send.go

if port == "465" {
		//via TLS
		conn, err := tls.Dial("tcp", addr, tlsConfig)
		if err != nil {
			return err
		}
		c, err = smtp.NewClient(conn, host)
		if err != nil {
			return err
		}
	} else {
		c, err = smtp.Dial(addr)
		if err != nil {
			return err
		}
	}
	defer c.Close()

	if err := c.Hello("localhost"); err != nil {
		return err
	}

	if port != "465" {
		if ok, _ := c.Extension("STARTTLS"); ok {
			if err := c.StartTLS(tlsConfig); err != nil {
				return err
			}
		}
	}

The code here uses port as a condition to determine whether to enable tls while we set it in other field actually.
Environment:

• TKE version:
• Global or business cluster:
• Kubernetes version (use kubectl version):
• Install addons:
• Others: