udev: add new builtin net_driver

Currently the ID_NET_DRIVER is set in net_setup_link builtin.
But this is called pretty late in the udev processing chain.

Right now in some custom rules it was workarounded by calling ethtool
binary directly, which is ugly.

So let's split this code to a separate builtin.

rules.d/50-udev-default.rules.in

@@ -26,6 +26,8 @@ ENV{MODALIAS}!="", IMPORT{builtin}="hwdb --subsystem=$env{SUBSYSTEM}"
 # To keep the backward compatibility, let's set ID_PATH for them.
 SUBSYSTEM=="pci|usb|platform", IMPORT{builtin}="path_id"
 
+SUBSYSTEM=="net", IMPORT{builtin}="net_driver"
+
 ACTION!="add", GOTO="default_end"
 
 SUBSYSTEM=="tty", KERNEL=="ptmx", GROUP="tty", MODE="0666"