We need to be able to go on constructing a complex filter in multiple
stages, since we can only set one filter per event.

For instance, we need to be able, in 'perf trace' to filter by the
'common_pid' field all the time, if only for the tracer itself, to
avoid a feedback loop, and, in addition, we may want to filter the
raw_syscalls:sys_{enter,exit} events by its 'id' filter, when using
'perf trace -e open,close' or 'perf trace -e !open,close', i.e. when
we are interested in just a subset of syscalls or when we are not
interested in it.

So we will have:

   perf_evsel__set_filter(evsel, char *filter)

       Replaces whatever is in evsel->filter.

   perf_evsel__append_filter(evsel, const char *op, char *filter)

       Appends, using op ("&&" or "||") with what is in evsel->filter.

   perf_evsel__apply_filter(evsel, filter):

        That actually applies a filter, be it the one being
        constructed in evsel->filter, or any other, for tools
        with more specific ways to build the filter, issuing
        the appropriate ioctl for all the evsel fds.

The same changes will be made to the evlist__{set,apply} variants to
keep everything consistent.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-2s5z9xtpnc2lwio3cv5x0jek@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>