help: Add -d option into usage output

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
docs: Document -d option

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
net: ifaddr -- Don't forget to hash read position

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>