[ldap] add support for ldapi:// URL #7737

Steps to reproduce

1. Install Nextcloud and a local ldap server.
2. Go to LDAP auth configuration.
3. Try to setup the server to use ldapi:// unix socket instead of ldap://

Actually, the underlying php ldap module properly support ldapi:// URI. The main issue is with the
user_ldap module forcing to set a port and always append the port to the ldap URI.

By relaxing the port requirement, I managed to setup a connection using ldapi:// url.

An other issue is that it look like the code path to check the configuration in the front-end is not the same than the one used when doing ldap:config-test.

When using ldapi:// URI, the front-end refuses to validate or detect the DN and always tell me there is a configuration issue, while running occ ldap:config-test report that connection is OK.

Expected behaviour

It should be possible to use ldapi URI for LDAP configuration and all LDAP features should work the same than when using ldap protocol.

Actual behaviour

ldapi can't be configured because the nextcloud code require a port settings and append it to the URI and even without that problem, the configuration panel remain broken.

Server configuration

Operating system:
Ubuntu Xenial

Web server:
NGINX

Database:
PostgreSQL

PHP version:
7.0

Nextcloud version: (see Nextcloud admin page)
12.0.4

Updated from an older Nextcloud/ownCloud or fresh install:
Fresh install

Where did you install Nextcloud from:
Command line

Signing status:

Login as admin user into your Nextcloud and access 
http://example.com/index.php/settings/integrity/failed 
paste the results here.

No errors have been found.

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/...

LDAP