selftests/zram: Skip max_comp_streams interface on newer kernel

selftests/zram: Skip max_comp_streams interface on newer kernel

Since commit 43209ea2d17a ("zram: remove max_comp_streams internals"), zram
has switched to per-cpu streams. Even kernel still keep this interface for
some reasons, but writing to max_comp_stream doesn't take any effect. So
skip it on newer kernel ie 4.7.

The code that comparing kernel version is from xfstests testsuite ext4/053.

Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>