net: use ethtool_cmd_speed_set helper to set ethtool speed value

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/intel/igb/igb_ethtool.c
Simple merge

diff --cc drivers/net/ntb_netdev.c
Simple merge

diff --cc drivers/s390/net/qeth_core_main.c
Simple merge