Backport of r47591 and r48427

This patch adds the kernel modules to for the very common Realtek RTL8150 and Realtek 8152 based USB-to-Ethernet converters.
After this patch the following packages can be added to targets (or site.mk):
kmod-usb-net-rtl8150
kmod-usb-net-rtl8152

The modules are already available in openwrt trunk, but not in Chaos Calmer. This patch is just a temporary backport.
The modules are needed for Futros with additional USB-Ethernet-Interface and VMs with dedicated USB-NIC