net: ieee802154: forbid monitor for add llsec seclevel

This patch forbids to add llsec seclevel for monitor interfaces which we
don't support yet. Otherwise we will access llsec mib which isn't
initialized for monitors.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210405003054.256017-14-aahringo@redhat.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl802154.c

@@ -2115,6 +2115,9 @@ static int nl802154_add_llsec_seclevel(struct sk_buff *skb,
 	struct wpan_dev *wpan_dev = dev->ieee802154_ptr;
 	struct ieee802154_llsec_seclevel sl;
 
+	if (wpan_dev->iftype == NL802154_IFTYPE_MONITOR)
+		return -EOPNOTSUPP;
+
 	if (llsec_parse_seclevel(info->attrs[NL802154_ATTR_SEC_LEVEL],
 				 &sl) < 0)
 		return -EINVAL;