Fix iSCSI portal create: remove port from listen entries

The TrueNAS API rejects port inside listen array items
(iscsi_portal_create.listen.0.port: Extra inputs are not permitted).
Port is a global iSCSI setting, not per-listen-IP.

- _iscsi_portal_payload(): strip port from each listen entry,
  keeping only {"ip": "..."}
- _prompt_iscsi_portals(): remove port prompt from wizard; show
  source IPs without port in the display

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

truenas_migrate/migrate.py

@@ -179,7 +179,10 @@ def _iscsi_initiator_payload(initiator: dict) -> dict:
 
 
 def _iscsi_portal_payload(portal: dict) -> dict:
-    return {k: v for k, v in portal.items() if k not in _ISCSI_PORTAL_READONLY}
+    payload = {k: v for k, v in portal.items() if k not in _ISCSI_PORTAL_READONLY}
+    # The API only accepts {"ip": "..."} in listen entries — port is a global setting
+    payload["listen"] = [{"ip": l["ip"]} for l in payload.get("listen", [])]
+    return payload
 
 
 def _iscsi_target_payload(