Implement LINKMODES_SET netlink request to set advertised linkmodes and
related attributes as ETHTOOL_SLINKSETTINGS and ETHTOOL_SSET commands do.

The request allows setting autonegotiation flag, speed, duplex and
advertised link modes.
Signed-off-by: NMichal Kubecek <mkubecek@suse.cz>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>