stack_guard_kernel does not work with zstd modules

[Thadeu Lima de Souza Cascardo]

The qrt kernel security test named stack_guard_kernel look for modules under /lib/modules/`uname -r`/ and tries to readelf them. That doesn't work for zstd compressed modules. Since readelf won't work with stdin, the test needs to be changed to copy the uncompressed module into a temporary location before doing a readelf.