Bluetooth: hci_event: Use of a function table to handle LE subevents

This change the use of switch statement to a function table which is
easier to extend and can include min/max length of each subevent.
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>