Update documentation for kernel command line ip.

The example leaves autoconfiguration set to on, this can cause
very long delays during boot.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>

docs/usb_moded-doc.txt

@@ -132,7 +132,7 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
 
 For more info see the kernel source: Documentation/filesystems/nfs/nfsroot.txt
 
-for example : ip=192.168.3.100::192.168.3.1:255.255.255.0::usb0:on
+for example : ip=192.168.3.100::192.168.3.1:255.255.255.0::usb0:off
 
 NOTE: The device must be usb0! The autoconf value is ignored.