Revert "pktgen: clean up ktime_t helpers"

This reverts commit 0f0c34b7c6c99c177764c8edcf5884ea0dd3eda5.
Revert "iopoll: Use ktime_get() instead of jiffies for timeout calculations"

This reverts commit c0d343b147659dc8329d27f9d7f1e5e181c058cc.