tracing: add missing include "log.hh"
tracing: add missing include "log.hh"

It's currently made available via another include, which is going away.

avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla