Bluetooth: hci_event: Use of a function table to handle HCI events

This change the use of switch statement to a function table
which is easier to extend and can include min/max length of each HCI
event.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>