In order to completely generalize the mgmt command handling we need to
move away command-specific information from mgmt_control() into the
actual command table. This patch adds a new 'flags' field to the handler
entries which can now contain the following command specific
information:

 - Command takes variable length parameters
 - Command doesn't target any specific HCI device
 - Command can be sent when the HCI device is unconfigured

After this the mgmt_control() function is completely generic and can
potentially be reused by new HCI channels.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>