netlink: specs: ovs: correct enum names in specs

Align the enum-names of OVS with what's actually in the uAPI.
Either correct the names, or mark the enum as empty because
the values are in fact #defines.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>