Bluetooth: HCI: Fix the length of supported commands

The length of the commands array in the return parameters of
the HCI Read Local Supported Commands event is 64 bytes
according to the spec. This was mistakenly set as 36 bytes due
to the fact that only 36 out of the 64 bytes currently contain
meaningful data. The actual array as received from the driver
will always be 64 bytes however, and is therefore sized
accordingly.

Change-Id: Iee7f1fc18045dff96efcc808fd81661eced37b03
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>