Bluetooth: Use GFP_KERNEL in hci_add_adv_entry()

This function is not called in interrupt context anymore, so it
should use GFP_KERNEL to allocate memory.

Signed-off-by: Andre Guedes <aguedespe@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>