usb: netusb: Add ethernet_init()

After PR #8608 every driver should call ethernet_init(), fixes missing
chunks of that PR.

Fixes: #8752

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>

subsys/usb/class/netusb/netusb.c

@@ -579,6 +579,8 @@ static void netusb_init(struct net_if *iface)
 
 	netusb.iface = iface;
 
+	ethernet_init(iface);
+
 	net_if_set_link_addr(iface, mac, sizeof(mac), NET_LINK_ETHERNET);
 
 	net_if_down(iface);