usb: android: lge: Enable RNDIS instead of ECM.

Vendor code uses ECM but this is not supported in the AOSP framework.

Disassociate USB_G_LGE_ANDROID from ECM/RNDIS and make ECM a separate
config option, USB_G_LGE_ECM (disabled by default).

Change-Id: I3c0e56ebd0d5ebc8b9b0b58f19108d23fe211ed3