I've noticed that /etc/udev/scripts/network.sh is not working anymore as expected within SDK 5.6.0.0.
Loading g_ether USB gadget module, or attaching a USB network device to USB host port, should cause the hotplugged usb0 interface to be configured properly (with dhcpc by default): this is what happens with SDK 5.5 but not with SDK 5.6.
The reasons are more than one. The ifup/ifdown are no more in the PATH when running the script. But first of all, the logic of the script is broken due to a different network init script (/etc/init.d/networking): the udev script relays on network init script and on /etc/network/options (missing in SDK 5.6) to make some assumptions and detect if it is invoked during udev init (in this case it has to do nothing) or after it (normal runtime condition, configure/deconfigure new hotplugged intefaces). Now it behaves always as in the first case.
BTW queueing interfaces to /dev/udev_network_queue seems useless since udev_network_queue.sh is missing or not used anymore (but this a minor issue present also in older SDK releases).
Max