Fix Ethernet documentation.

1. Remove incorrect @return tag for void function.
2. Fix build breakage by removing the reference to
   #ETHERNET_SERVICE, which is hidden.

Change-Id: Ia893464bafc8257e48e0bd710d27954b535fcece
(cherry picked from commit ff7e406df8a46256e47fff70abc9116ad3f94c23)

core/java/android/content/Context.java

@@ -1994,6 +1994,7 @@ public abstract class Context {
             WIFI_PASSPOINT_SERVICE,
             WIFI_P2P_SERVICE,
             WIFI_SCANNING_SERVICE,
+            //@hide: ETHERNET_SERVICE,
             NSD_SERVICE,
             AUDIO_SERVICE,
             MEDIA_ROUTER_SERVICE,
@@ -2069,9 +2070,6 @@ public abstract class Context {
      *  <dt> {@link #WIFI_P2P_SERVICE} ("wifip2p")
      *  <dd> A {@link android.net.wifi.p2p.WifiP2pManager WifiP2pManager} for management of
      * Wi-Fi Direct connectivity.
-     *  <dt> {@link #ETHERNET_SERVICE} ("ethernet")
-     *  <dd> A {@link android.net.ethernet.EthernetManager EthernetManager} for
-     * management of Ethernet connectivity.
      * <dt> {@link #INPUT_METHOD_SERVICE} ("input_method")
      * <dd> An {@link android.view.inputmethod.InputMethodManager InputMethodManager}
      * for management of input methods.

core/java/android/net/EthernetManager.java

@@ -47,7 +47,7 @@ public class EthernetManager {
     }
 
     /**
-     * Get Ethernet configuration
+     * Get Ethernet configuration.
      * @return the Ethernet Configuration, contained in {@link IpConfiguration}.
      */
     public IpConfiguration getConfiguration() {
@@ -61,8 +61,7 @@ public class EthernetManager {
     }
 
     /**
-     * Set Ethernet configuration
-     * @return true if setting success
+     * Set Ethernet configuration.
      */
     public void setConfiguration(IpConfiguration config) {
         try {