ethtool: set pause parameters with PAUSE_SET request

Implement PAUSE_SET netlink request to set pause parameters of a network
device. Thease are traditionally set with ETHTOOL_SPAUSEPARAM ioctl
request.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>