Bluetooth: Add MGMT capability flags for tx power and ext advertising

For new advertising features, it will be important for userspace to
know the capabilities of the controller and kernel. If the controller
and kernel support extended advertising, we include flags indicating
hardware offloading support and support for setting tx power of adv
instances.

In the future, vendor-specific commands may allow the setting of tx
power in advertising instances, but for now this feature is only
marked available if extended advertising is supported.

This change is manually verified in userspace by ensuring the
advertising manager's supported_flags field is updated with new flags on
hatch chromebook (ext advertising supported).

Signed-off-by: Daniel Winkler <danielwinkler@google.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>