Fix MTU=0 validation and create_message_chunks import errors

- Send mtu=None instead of mtu=0 (NetBox requires MTU >= 1)
- Remove create_message_chunks usage (not in installed SDK version)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

collectors/network_collector.py

@@ -1052,7 +1052,7 @@ def build_interface_entities(interfaces: dict, hostname: str, model: str,
             name=name,
             type=iface_type,
             enabled=iface_data.get("is_enabled", True),
-            mtu=int(iface_data.get("mtu") or 0),
+            mtu=int(iface_data["mtu"]) if iface_data.get("mtu") else None,
             speed=int(speed * 1000) if speed else 0,  # NAPALM Mbps → NetBox Kbps
             description=iface_data.get("description") or "",
             tags=["network-collector"],

collectors/pbs_collector.py

@@ -271,7 +271,7 @@ def build_interface_entities(hostname: str, interfaces: list[dict],
             name=name,
             type=_map_interface_type(pve_type, name),
             enabled=bool(iface.get("active", 0)),
-            mtu=iface.get("mtu"),
+            mtu=int(iface["mtu"]) if iface.get("mtu") else None,
             description=", ".join(desc_parts)[:200] if desc_parts else "",
             tags=["proxmox", "pbs"],
         )))