Silence some "unchecked return-value" warnings

Silence some "unchecked return-value" warnings

This adds some log-messages to ioctl() calls where we don't really care
for the return value. It isn't strictly necessary to look for those, but
lets be sure and print warnings. This silences gcc and coverity, and also
makes sure we get reports in case something goes wrong and we didn't
expect it to fail that way.