netlink: Remove compat API for nested attributes

Removes all _nested_compat() functions from the API. The prio qdisc
no longer requires them and netem has its own format anyway. Their
existance is only confusing.

Resend: Also remove the wrapper macro.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>