options: convert

Sorry this one has a bug also - it compresses a signed 64 bit quantity into a 32-bit unsigned value. When re-interpreted as microsecond value (in dccp_sample_rtt), this gives values which are way too small.

Maybe we should keep the dccp_epoch thing, but now with ktime_t, so as to avoid large microsecond values?

In any case, the RTT sampling is not usable - it constantly produces overflow, since the timestamp option value is too small.