net: cdc_ncm: Fix build error

If USB_NET_CDC_NCM is y and USB_NET_CDCETHER is m, build fails:

drivers/net/usb/cdc_ncm.o:(.rodata+0x1d8): undefined reference to `usbnet_cdc_update_filter'

Select USB_NET_CDCETHER for USB_NET_CDC_NCM to fix this.
Reported-by: NHulk Robot <hulkci@huawei.com>
Fixes: e10dcb1b ("net: cdc_ncm: hook into set_rx_mode to admit multicast traffic")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/Kconfig

@@ -252,6 +252,7 @@ config USB_NET_CDC_EEM
 config USB_NET_CDC_NCM
 	tristate "CDC NCM support"
 	depends on USB_USBNET
+	select USB_NET_CDCETHER
 	default y
 	help
 	  This driver provides support for CDC NCM (Network Control Model