Validate enable-isolation with shared and bridged modes

[nirs]

Summary

Currently we reject --enable-isolation without --operation-mode=host, but this is not documented behavior. We should validate whether isolation actually works with shared and bridged modes.

Background

The vmnet_enable_isolation_key documentation states:

Interface isolation ensures that network communication between multiple vmnet_interface instances is not possible.

This suggests isolation might work for any mode by isolating interfaces from each other, not just for host mode.

Current behavior

• Host mode: --enable-isolation is allowed
• Shared mode: --enable-isolation is rejected
• Bridged mode: --enable-isolation is rejected

Tasks

• Test --enable-isolation with shared mode
• Test --enable-isolation with bridged mode
• If it works, update options.c to allow it
• If it fails, document why in a comment