Bluetooth: Add read_version management command

This patch implements the initial read_version command that userspace
will use before any other management interface operations.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>