dpif-netdev: Move 'struct dp_netdev_port' initialization before use.

dpif-netdev: Move 'struct dp_netdev_port' initialization before use.

There is a portion of the 'struct dp_netdev_port' initialization
that is placed after the reload of pmd threads.  This means in
theory, there could be a race where pmd threads access half-
initialized struct.  Although such race has not been seen, it
makes sense to fully initialize the struct before use.

Found by code inspection.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>