Bluetooth: hci_event: Fix HCI_EV_VENDOR max_len

HCI_EV_VENDOR is in fact variable length since it acts as metaevent
where a vendor can implement their own event sets.

In addition to it this makes use of bt_dev_warn_ratelimited to supress
the amount of logging in case the event has more data than expected.

Fixes: 3e54c589 ("Bluetooth: hci_event: Use of a function table to handle HCI event")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>