net: ieee802154: forbid monitor for set llsec params

This patch forbids to set llsec params for monitor interfaces which we
don't support yet.

Reported-by: syzbot+8b6719da8a04beeafcc3@syzkaller.appspotmail.com
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210405003054.256017-3-aahringo@redhat.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl802154.c

@@ -1384,6 +1384,9 @@ static int nl802154_set_llsec_params(struct sk_buff *skb,
 	u32 changed = 0;
 	int ret;
 
+	if (wpan_dev->iftype == NL802154_IFTYPE_MONITOR)
+		return -EOPNOTSUPP;
+
 	if (info->attrs[NL802154_ATTR_SEC_ENABLED]) {
 		u8 enabled;