netlink: specs: decode indirection table as u32 array

Indirection table is dumped as a raw u32 array, decode it.
It's tempting to decode hash key, too, but it is an actual
bitstream, so leave it be for now.

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