docs: networking: dpaa2: Fix DPNI header

The DPNI object should get its own header, like the rest of the objects.

Fixes: 60b91319 ("staging: fsl-mc: Convert documentation to rst format")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/device_drivers/ethernet/freescale/dpaa2/overview.rst

@@ -183,6 +183,7 @@ PHY and allows physical transmission and reception of Ethernet frames.
   IRQ config, enable, reset
 
 DPNI (Datapath Network Interface)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Contains TX/RX queues, network interface configuration, and RX buffer pool
 configuration mechanisms.  The TX/RX queues are in memory and are identified
 by queue number.