Bluetooth: MGMT: Fix MGMT_OP_ADD_DEVICE invalid device flags

Device flags could be updated in the meantime while MGMT_OP_ADD_DEVICE
is pending on hci_update_passive_scan_sync so instead of setting the
current_flags as cmd->user_data just do a lookup using
hci_conn_params_lookup and use the latest stored flags.

Fixes: a182d9c8 ("Bluetooth: MGMT: Fix Add Device to responding before completing")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>