Bluetooth: Add support for setting LE advertising data

This patch adds support for setting basing LE advertising data. The
three elements supported for now are the advertising flags, the TX power
and the friendly name.

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>