Bluetooth: Remove "Power-on" check from Mesh feature

The Bluetooth mesh experimental feature enable was requiring the
controller to be powered off in order for the Enable to work. Mesh is
supposed to be enablable regardless of the controller state, and created
an unintended requirement that the mesh daemon be started before the
classic bluetoothd daemon.

Fixes: af6bcc19 ("Bluetooth: Add experimental wrapper for MGMT based mesh")
Signed-off-by: Brian Gix <brian.gix@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>