While investigating the reported hostcache
issues and adding a histogram to look at the
distribution of used hashbuckets, and
bucketdepth, I found that the exteremly
fast XOR "hash" would result in a rather
skewed utilization of the hostcache, for
randomly selected remote IP addresses.
As other parts of the base tcp stack (eg.
tcp fastopen) already use jenkins_hash32,
and the properties appear reasonably good,
switching to use that.