ipc: simplify message copying

ipc: simplify message copying

Remvoe the redundant and confusing fill_copy().  Also add copy_msg() check
for error.  In this case exit from the function have to be done instead of
break, because further code interprets any error as EAGAIN.

Also define copy_msg() for the case when CONFIG_CHECKPOINT_RESTORE is
disabled.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>