The data items returned by netdev_get_devices() are "struct netdev *"s.
The code fixed up by this commit used them as "struct netdev_linux *",
which happens to work because struct netdev happens to be at offset 0 in
each struct but it's better to do a proper cast in case someday
struct netdev gets moved to a nonzero offset.
Signed-off-by: Ben Pfaff <blp@nicira.com>