When CONFIG_IPC_NS=n, clone(CLONE_NEWIPC) claims success, but did not actually
clone a new IPC namespace.

Fix this to return -EINVAL so the caller knows his request was denied.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>