ethtool: link up ethnl_header_policy as a nested policy

To get the most out of parsing by the core, and to allow dumping
full policies we need to specify which policy applies to nested
attrs. For headers it's ethnl_header_policy.

$ sed -i 's@\(ETHTOOL_A_.*HEADER\].*=\) { .type = NLA_NESTED },@\1\n\t\tNLA_POLICY_NESTED(ethnl_header_policy),@' net/ethtool/*

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>