Bluetooth: Use GFP_KERNEL in hci_conn_add()

This function is called in process context only, so it should use
GFP_KERNEL to allocate memory.

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