Fix delay filter validation: ensure delay: [0, X] returns proper error message

This fix addresses the issue where delay: [0, X] configurations were being
silently dropped instead of returning validation errors.

Changes:
- Created new utility function filter_inactive_filters() in packet_filter_validation.py
- Implemented smart filtering logic for delay filter that checks both latency and jitter:
  * delay: [0, 0] → User wants to disable delay, filter out silently
  * delay: [0, X] where X > 0 → Invalid config, keep for validation error
  * delay: [X, X] where X > 0 → Normal configuration, validate normally
- Simplified link.py update_filters() method to use the new utility function
- Added comprehensive tests for the new filtering logic

Before this fix:
- delay: [0, 100] would be silently dropped with no error message
- Users wouldn't know their configuration was invalid

After this fix:
- delay: [0, 100] returns proper error: "delay parameter Latency must be between 1 and 32767 ms, got: 0"
- delay: [0, 0] is correctly handled as intentional disable
- Normal delay configurations continue to work as expected

gns3server/controller/link.py

@@ -23,7 +23,7 @@ import html
 from .controller_error import ControllerError, ControllerNotFoundError
 from gns3server.agent.web_wireshark.manager import WebWiresharkManager
 from gns3server.config import Config
-from gns3server.utils.packet_filter_validation import validate_all_filters, FilterValidationError
+from gns3server.utils.packet_filter_validation import validate_all_filters, filter_inactive_filters, FilterValidationError
 
 import logging
 
@@ -148,19 +148,11 @@ class Link:
         """
         Modify the filters list.
 
-        Filter with value 0 will be dropped because not active
+        Filters with value 0 will be filtered out as inactive, with special
+        handling for delay filter to distinguish between "disabled" and "invalid config".
         """
-        new_filters = {}
-        for (filter, values) in filters.items():
-            new_values = []
-            for value in values:
-                if isinstance(value, str):
-                    new_values.append(value.strip("\n "))
-                else:
-                    new_values.append(int(value))
-            values = new_values
-            if len(values) != 0 and values[0] != 0 and values[0] != "":
-                new_filters[filter] = values
+        # Filter out inactive filters using the utility function
+        new_filters = filter_inactive_filters(filters)
 
         # Validate filter parameters before applying
         try: