Problem description: in section "Zabbix server details" of Zabbix installation form, it is possible to enter a port number in field "Port" that is out of the existing port range, for example "99999". There should be a validation that checks if the entered port number is not higher than 65535 (like it is done in "Configure DB connection" section).

Steps to reproduce:

1. Open Zabbix installation form (setup.php)
2. Proceed to "Zabbix server sdetails" section 
3. Enter a 5 digit port number in field "Port" that is higher than 65535
4. Press "Next step" button

Result: next installation section is displayed even though the entered port number cannot possible exist.
Expected: There should be a validation that checks if the entered port number is not higher than 65535.