fix: set listen IP in _action_fix_snmp so snmpd binds to management IF

Without an explicit listen address, os-net-snmp on OPNsense may not
respond on non-loopback interfaces. The fix sets
listen = {self.hostname: {"selected": 1}} which is always the
management IP used to reach this device in netOrk.

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

napalm_opnsense/opnsense.py

@@ -1579,6 +1579,12 @@ class OPNsenseDriver(FirewallDriver):
             lines.append("[install] os-net-snmp already installed — skipping reinstall")
 
         # 2. Configure SNMP
+        # The listen field must contain the management IP so that snmpd binds
+        # to the correct interface. Without it snmpd may not respond on any
+        # non-loopback address.
+        # The API expects {"<ip>": {"selected": 1}} — we use self.hostname
+        # which is always the device's management IP in netOrk.
+        listen_val: dict = {self.hostname: {"selected": 1}}
         try:
             self._post("/api/netsnmp/general/set", {
                 "general": {
@@ -1588,9 +1594,10 @@ class OPNsenseDriver(FirewallDriver):
                     "location": "Managed by netOrk",
                     "sysobjid": "",
                     "bindip": "",
+                    "listen": listen_val,
                 }
             })
-            lines.append("[config] SNMP enabled with community 'public'.")
+            lines.append(f"[config] SNMP enabled with community 'public', listen={self.hostname}.")
         except Exception as exc:
             logger.debug("SNMP config failed: %s", exc)
             lines.append(f"[config] error: {exc}")