network scan fails when using very large subnets

[cotosso]

Brief description
When performing a network scan on very large subnets, such as a /16, the UI eventually reports errors while the scan is running.

Steps to reproduce

1. Configure a network scan on a /16 subnet
2. Start the scan from the UI.
3. After some time, the UI begins to display errors.

Expected behavior
The UI should handle long-running scans gracefully without showing errors.

Actual behavior
UI errors appear during the scan of large subnets.

Proposed solution
Instead of showing UI errors, display an informative message indicating that scanning is supported for /20 networks at maximum.

Components

NethSecurity 8.7.1