Add EthernetDevice to manage ethernet connection.

The current fastbootd only supports USB protocol. But some Android TV
devices are built without USB port. The fastbootd cannot be used on
those ATV devices due to it. aosp/1295566 enables fastbootd over
ethernet.

This change adds an EthernetDevice to manage ethernet connection and set
fastbootd protcol property fastbootd.protocol to enable fastbootd over
ethernet in recovery mode. It uses IPv6 link-local address to not expose
the devices out of the network segment. The devices who want to use this
EthernetDevice should add
“TARGET_RECOVERY_UI_LIB := librecovery_ui_ethernet” into BoardConfig.mk.

BUG: 152544169
BUG: 155198345
Test: Enter and exit fastboot mode and check eth0 IPv6 link-local address
on screen UI.

Change-Id: I73fe44be3790bdba5a6059fbba3f7264b21eed99
Merged-In: I73fe44be3790bdba5a6059fbba3f7264b21eed99
diff --git a/recovery_main.cpp b/recovery_main.cpp
index 30a1fc0..80cba61 100644
--- a/recovery_main.cpp
+++ b/recovery_main.cpp
@@ -471,6 +471,11 @@
     std::string usb_config =
         fastboot ? "fastboot" : IsRoDebuggable() || IsDeviceUnlocked() ? "adb" : "none";
     std::string usb_state = android::base::GetProperty("sys.usb.state", "none");
+    if (fastboot) {
+      device->PreFastboot();
+    } else {
+      device->PreRecovery();
+    }
     if (usb_config != usb_state) {
       if (!SetUsbConfig("none")) {
         LOG(ERROR) << "Failed to clear USB config";