A reliable way for userspace to check if a msg is from kernel
- IPC_FLG_MSG_FROM_KERNEL status flag is returned to userspace if the
receive was satisfied by s message which was sent by the kernel on
behalf of a process. This perfectly reliale information.
- MF_SENDING_FROM_KERNEL flag added to processes to be able to set
IPC_FLG_MSG_FROM_KERNEL when finishing receive if the receiver
wasn't ready to receive immediately.
- PM is changed to use this information to confirm that the scheduling
messages are indeed from the kernel and not faked by a process.
PM uses sef_receive_status()
- get_work() is removed from PM to make the changes simpler
