Revert unrelated changes for SMTP auth (#21767) (#21768)

Backport #21767

The purpose of #18982 is to improve the SMTP mailer, but there were some
unrelated changes made to the SMTP auth in
https://github.com/go-gitea/gitea/pull/18982/commits/d60c43869420f5fc43ad19b454c9ae50dad65964

This PR reverts these unrelated changes, fix #21744

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

services/auth/source/smtp/auth.go

@@ -58,10 +58,10 @@ var ErrUnsupportedLoginType = errors.New("Login source is unknown")
 func Authenticate(a smtp.Auth, source *Source) error {
 	tlsConfig := &tls.Config{
 		InsecureSkipVerify: source.SkipVerify,
-		ServerName:         source.Addr,
+		ServerName:         source.Host,
 	}
 
-	conn, err := net.Dial("tcp", net.JoinHostPort(source.Addr, strconv.Itoa(source.Port)))
+	conn, err := net.Dial("tcp", net.JoinHostPort(source.Host, strconv.Itoa(source.Port)))
 	if err != nil {
 		return err
 	}
@@ -71,7 +71,7 @@ func Authenticate(a smtp.Auth, source *Source) error {
 		conn = tls.Client(conn, tlsConfig)
 	}
 
-	client, err := smtp.NewClient(conn, source.Addr)
+	client, err := smtp.NewClient(conn, source.Host)
 	if err != nil {
 		return fmt.Errorf("failed to create NewClient: %w", err)
 	}

services/auth/source/smtp/source.go

@@ -19,7 +19,7 @@ import (
 // Source holds configuration for the SMTP login source.
 type Source struct {
 	Auth           string
-	Addr           string
+	Host           string
 	Port           int
 	AllowedDomains string `xorm:"TEXT"`
 	ForceSMTPS     bool

services/auth/source/smtp/source_authenticate.go

@@ -32,7 +32,7 @@ func (source *Source) Authenticate(user *user_model.User, userName, password str
 	var auth smtp.Auth
 	switch source.Auth {
 	case PlainAuthentication:
-		auth = smtp.PlainAuth("", userName, password, source.Addr)
+		auth = smtp.PlainAuth("", userName, password, source.Host)
 	case LoginAuthentication:
 		auth = &loginAuthenticator{userName, password}
 	case CRAMMD5Authentication: