Bluetooth: controller: Fix accept scan en/disable if already en/disabled

Conform to Bluetooth Specification, if the LE_Scan_Enable
parameter is set to 0x01 and scanning is already enabled,
any change to the Filter_Duplicates setting shall take
effect. Disabling scanning when it is disabled has no
effect.

Fixes #31019.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>