usbnet: CDC EEM support (v5)

This introduces a CDC Ethernet Emulation Model (EEM) host side
driver to support USB EEM devices.

EEM is different from the Ethernet Control Model (ECM) currently
supported by the "CDC Ethernet" driver.  One key difference is
that it doesn't require of USB interface alternate settings to
manage interface state; some maldesigned hardware can't handle
that part of USB.  It also avoids a separate USB interface for
control and status updates.

[ dbrownell@users.sourceforge.net: fix skb leaks, add rx packet
checks, improve fault handling, EEM conformance updates, cleanup ]

Signed-off-by: Omar Laazimani <omar.oberthur@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/Kconfig

@@ -180,6 +180,20 @@ config USB_NET_CDCETHER
 	  IEEE 802 "local assignment" bit is set in the address, a "usbX"
 	  name is used instead.
 
+config USB_NET_CDC_EEM
+	tristate "CDC EEM support"
+	depends on USB_USBNET && EXPERIMENTAL
+	help
+	  This option supports devices conforming to the Communication Device
+	  Class (CDC) Ethernet Emulation Model, a specification that's easy to
+	  implement in device firmware.  The CDC EEM specifications are available
+	  from <http://www.usb.org/>.
+
+	  This driver creates an interface named "ethX", where X depends on
+	  what other networking devices you have in use.  However, if the
+	  IEEE 802 "local assignment" bit is set in the address, a "usbX"
+	  name is used instead.
+
 config USB_NET_DM9601
 	tristate "Davicom DM9601 based USB 1.1 10/100 ethernet devices"
 	depends on USB_USBNET