Bluetooth: Mesh: Scanner is enabled during Friendship termination

Scanner was disabled after Friend Clear command. LNP didn't have
chance to receive Friend Clear Confirmation command back.
If option BT_MESH_LPN_ESTABLISHMENT is off then scanner is left
disabled and next Friend Offer after Friend Request
cannot be received.
PR fixes this.

Signed-off-by: Aleksandr Khromykh <aleksandr.khromykh@nordicsemi.no>