different default values are used for parameter 'mail_smtpmode`

[j-ed]

refers to #3069

Expected behavior

For all parameters default values should be set and the same default value should be used for all appearances in the source code.

Current behavior

Not all of the parameters are set to a fixed default value, nor have they the same default value assigned in the source code.

As far as I understood the default value of the parameter mail_smtpmode should be sendmail but other values have been assigned in the source code:

+ getSystemValue('mail_smtpmode', 'sendmail')       # ok, default value !!
- /var/www/htdocs/nextcloud/lib/private/Mail/Mailer.php:203

+ getSystemValue('mail_smtpmode', 'php')            # <<< wrong value, should be 'sendmail'
- /var/www/htdocs/nextcloud/lib/private/Mail/Mailer.php:156

+ getSystemValue('mail_smtpmode', '')               # <<< wrong value, should be 'sendmail'
- /var/www/htdocs/nextcloud/lib/private/Settings/Admin/Additional.php:58

Steps to reproduce

1. search and compare the assigned values in the getSystemValue() call.

Environment

Server Configuration

OS: Linux 3.2.82
Web server: Apache2 2.4.25
Database: MariaDB 5.5.53
PHP version: 5.6.29
Nextcloud version: 11.0.0

Client Configuration

Browser: Mozilla Firefox 50.1.0
Operating system: Windows 7

[MorrisJobke]

Fix is in #3177