perf hists: Don't decay total_period for filtered entries

Following the 'perf report' model we don't zap hist_entry instances from
the rb tree, we just keep them with he->filtered set to a mask of the
filters applied to it (thread, parent, DSO so far).

In top we need to decay even filtered entries, but we better not touch
total_period for them...

Now everything seems to work when filters are applied on top as they
worked in 'report', i.e. both dynamic and static hist entry browsing
works with filters.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-yt4xsbq20u9x9ypuwwyw2kao@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>