fix a couple of retors
message.c: start validating the user data sent to us

We need to still do more, but it's a start.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kdbus_internal.h: start to think about how we are going to handle fds

I can't believe I'm actually implementing a feature that I think is one
of the craziest UNIX features ever...

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>