enable_event: append to set_event, to avoid disabling previous events.
enable_event: append to set_event, to avoid disabling previous events.

Writing to set_event, rather than appending, disables all other events
first.

Signed-off-by: Josh Triplett <c028c213ed5efcf30c3f4fc7361dbde0c893c5b7@joshtriplett.org>

bigzz/trace-cmd,bigzz/trace-cmd