Bluetooth: host: Rename and make non-static HCI cmd state update

Enable CTE HCI command requires update of a state of its
execution after receive command completion response from
controller. Host has already implemented such functionality
but it was used only internally by hci_core.

This commit changes it to be accessible from other sourece files
in host.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>