fix: AOS-Switch REST API session cookie auth and VLAN PUT body

connect() never sent back the sessionId returned in the login response
body, so all writes (POST/PUT/DELETE) were silently rejected with
"Access is unauthorized" while reads worked fine. Also fix
_api_set_vlan to PUT the full VLAN object (AOS-Switch v3 rejects
partial PUT bodies with HTTP 400).

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

napalm_procurve/api_client.py

@@ -127,6 +127,13 @@ class ProcurveApiClient:
             raise ConnectAuthError(
                 f"REST API login failed (HTTP {resp.status_code}) for {self.hostname}"
             )
+        # AOS-Switch returns the session cookie in the JSON body rather than
+        # via Set-Cookie — it must be sent back as a Cookie header on every
+        # subsequent request, otherwise writes (POST/PUT/DELETE) are rejected
+        # with "Access is unauthorized" while reads still succeed.
+        cookie = resp.json().get("cookie")
+        if cookie:
+            self._session.headers.update({"Cookie": cookie})
         logger.debug("REST API login OK for %s", self.hostname)
 
     def setup(self, api_version: str, proto: str) -> None: