backports: handle new get_ts_info pointer in struct ethtool_ops

backports: handle new get_ts_info pointer in struct ethtool_ops

In kernel 3.5 struct ethtool_ops received a new function pointer
get_ts_info. Address this by putting ifdef around the code.

commit c8f3a8c31069137fe0100e6920558f1a7487ef3c
Author: Richard Cochran <richardcochran@gmail.com>
Date:   Tue Apr 3 22:59:17 2012 +0000

    ethtool: Introduce a method for getting time stamping capabilities.

git describe --contains c8f3a8c31069137fe0100e6920558f1a7487ef3c
v3.5-rc1~109^2~632

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>