logcat: add 'kernel' to defaults

I'm asked at least once a week or more why a new service isn't starting.
Usually, the reason is that "File ... has incorrect label or no domain
transition from ... to another SELinux domain defined. ..." from init.
Even in permissive mode, this is required.

Bug: 63014404
Test: boot, check logcat
Change-Id: I7244a56fc46f84e9592e1eccf2d23461691965b3