This message is shown if fcntl() fails (for any reason)

	ioping: fcntl failed, please retry without -D: Invalid argument

First, it tells that -D is invalid argument, which is misleading.

Second it tells to retry with -D even if -D was not used.

Fix it, now the message is:

	ioping: fcntl failed: Invalid argument
	Please retry without -D
Signed-off-by: Kir Kolyshkin <kir@openvz.org>