* Remove Compress by default

Set Compress = true in Scrub only when the message doesn not fit the
advertized buffer. Doing compression is expensive, so try to avoid it.

Master vs this branch
pkg: github.com/coredns/coredns/plugin/cache
BenchmarkCacheResponse-2   	   50000	     24774 ns/op

pkg: github.com/coredns/coredns/plugin/cache
BenchmarkCacheResponse-2   	  100000	     21960 ns/op

* and make it compile