sendfile08: disable this test on kernel less than 2.6.33

After kernel commit cc56f7d, sendfile(2) can support any file refered
"out_fd" instead of only socket.
Since this test for general file refered "out_fd", so we disable this
test on the kernel less than 2.6.33.

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Reviewed-by: Jan Stancek <jstancek@redhat.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>