EX-3937 lnet: include linux/ethtool.h

EX-3937 lnet: include linux/ethtool.h

Commit a8929b9f0b3e86ae91fd0037edc37a356020a947 added
a check to see if linux/ethtool.h is included in
linux/netdevice.h. However, a more simple way is to
include linux/ethtool.h directly in the files that use
"struct ethtool_ops".

Test-Parameters: trivial

Fixes: a8929b9f0b3 ("EX-3937 lnet: check if ethtool.h is included in netdevice.h")
Change-Id: I5d1b45a15194a0ba2dbd52ce47fdb9bf9fda028c
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45110
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>