Bluetooth: Refactor arguments of mgmt_device_connected

The values of a lot of the mgmt_device_connected() parameters come
straight from a hci_conn object. We can simplify the function by passing
the full hci_conn pointer to it.

Signed-off-by: Alfonso Acosta <fons@spotify.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>