Bluetooth: mgmt: Fix device_connected sending order

The mgmt_ev_device_connected signal must be sent before any event
indications happen for sockets associated with the connection. Otherwise
e.g. device authorization for the sockets will fail with ENOTCONN as
user space things that there is no baseband link.

This patch fixes the issue by ensuring that the device_connected event
if sent (if it hasn't been so already) as soon as the first ACL data
packet arrives from the remote device.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>