procd: Set /dev/kmsg to 600

procd: Set /dev/kmsg to 600

Small cleanup. I initially though /dev/kmsg was used for dmsg(and journald
on desktops) but this seems not to be the case. dmsg is still accessible
as non-root(gives output) which begs the question what does this do? Some
googling reveals that permissions are set to 600 for some embedded systems
while 644 for others. I can't find any justification for the latter. Might
as well err on the side of caution.

Signed-off by: Rosen Penev <rosenp@gmail.com>