Bluetooth: mgmt: Initialize HCI_MGMT flag for any command

The read_controller_info is typically the first command that user space
sends when taking a controller into use. This is also the reason why
this command has been used as the trigger to set the HCI_MGMT flag.
However, when not running the user-space daemon and using command line
tools it is possible that read_controller_info is not the first
controller specific command. This patch moves the HCI_MGMT
initialization to a generic place where it will be set for whatever
happens to be the first mgmt command targetting a specific controller.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>