If GRO offload is fixed in the wrong state, skip the tests.

1. Now tests can be skippable.
2. test_run.conf can include warning message
3. Only required offloads are set when relevant tests start.
4. If offload is fixed to wrong state test fails.
5. Offloads settings are read from system core instead of ethtool for <=6.2.
  1. Kernel 2.6.x, which used for XS <=6.2, does not have information inside for ethtool to function. Hence we cannot rely on information from ethtool.
  2. /sys/class/net/ethX/features have offloads setting information.
  3. Values can be found from: http://lxr.free-electrons.com/source/include/linux/netdevice.h?v=2.6.39#L1044
6. none-required test failure won't affect certification.