teamd: Don't ever kill PID 0

It's a suicide. daemon_pid_file_is_running() may return 0 in case a PID file
exists but is empty. It's safe to assume the daemon is not running -- it either
lost race while dying between opening and writing a PID file, or the system
crashed.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>