Stop any running DHCP client before bringup up an Ethernet interface

If the system server is restarted, the dhcpcd_eth0 service may have already
been started by the previous system server, and the new system server's
attempts to start the dhcpcd will do nothing.

Change-Id: Icfd480a5369eb9c7dfe86b43190294871a915529

core/java/android/net/EthernetDataTracker.java

@@ -221,6 +221,10 @@ public class EthernetDataTracker implements NetworkStateTracker {
                             mNetworkInfo.setExtraInfo(mHwAddr);
                         }
                     }
+
+                    // if a DHCP client had previously been started for this interface, then stop it
+                    NetworkUtils.stopDhcp(mIface);
+
                     reconnect();
                     break;
                 }