Bluetooth: Add setting of the LE event mask

This patch adds setting of the LE event mask to the HCI init procedure
for LE-capable controllers. Right now we only set the default mask which
is good enough for the events available in the 4.0 core specification.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>