switchdev: don't use anonymous union on switchdev attr/obj structs

Older gcc versions (e.g.  gcc version 4.4.6) don't like anonymous unions
which was causing build issues on the newly added switchdev attr/obj
structs.  Fix this by using named union on structs.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Reported-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>