Bluetooth: Reduce critical region.

This patch reduces the critial region (protected by hdev->lock) in
hci_cc_le_set_scan_enable(). This way, only really required code is
synchronized.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>