os-udpbroadcastrelay: relay port validation error (listen port already in use)

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Describe the bug
Trying to configure a second instance using the same relay port but with different instance ID and different interfaces results in a form validation error: "Listen port already in use".

To Reproduce
Steps to reproduce the behavior:

1. Install plugin os-udpbroadcastrelay
2. Add new instance with relay port 5353, instance id 1, multicast address 224.0.0.251, relay interfaces IF_1 and IF_2 and save.
3. Add a second instance with relay port 5353, instance id 2, multicast address 224.0.0.251, relay interfaces IF_3 and IF_4 and save.
4. See error: Listen Port already in use.

Expected behavior
Since the instance ID and interfaces are different, no error about the relay port should be displayed. Manual configuration via SSH with the same parameters results in a working setup with no errors.

Screenshots

Environment
os-udpbroadcastrelay version: 1.0_6
OPNsense version: 26.1.6

Workaround
Saving the new instance with a random port and then manually editing the /conf/config.xml file changing the port to the desired one resolves the issue (but you have to reboot opnsense to apply the config and then you still cannot edit the relay instance via web GUI without getting the error again).

Start by inspecting the os-udpbroadcastrelay instance configuration and its listen-port validation, then reproduce the two-instance setup in the web UI using the steps above. Done means separate instances with different IDs and interfaces can save using the same relay port without a validation error, while the configuration remains usable.