SocketImpl#getFileDescriptor shouldn't be public

It's protected, as it was before openJdk switch. Added
hidden public method getFD$ for tests.

Bug: 26689841
Change-Id: I7e4149a5100b448e8729536f9718a35707a1c290
diff --git a/luni/src/test/java/libcore/io/OsTest.java b/luni/src/test/java/libcore/io/OsTest.java
index d2c4058..552c2a1 100644
--- a/luni/src/test/java/libcore/io/OsTest.java
+++ b/luni/src/test/java/libcore/io/OsTest.java
@@ -49,7 +49,7 @@
     fis.close();
 
     ServerSocket s = new ServerSocket();
-    assertTrue(S_ISSOCK(Libcore.os.fstat(s.getImpl().getFileDescriptor()).st_mode));
+    assertTrue(S_ISSOCK(Libcore.os.fstat(s.getImpl().getFD$()).st_mode));
     s.close();
   }
 
diff --git a/luni/src/test/java/libcore/java/io/FileDescriptorTest.java b/luni/src/test/java/libcore/java/io/FileDescriptorTest.java
index adaa931..3e82690 100644
--- a/luni/src/test/java/libcore/java/io/FileDescriptorTest.java
+++ b/luni/src/test/java/libcore/java/io/FileDescriptorTest.java
@@ -37,7 +37,7 @@
     fis.close();
 
     ServerSocket s = new ServerSocket();
-    assertTrue(s.getImpl().getFileDescriptor().isSocket$());
+    assertTrue(s.getImpl().getFD$().isSocket$());
     s.close();
   }
 }
diff --git a/ojluni/src/main/java/java/net/SocketImpl.java b/ojluni/src/main/java/java/net/SocketImpl.java
index 18044ab..d2123e2 100755
--- a/ojluni/src/main/java/java/net/SocketImpl.java
+++ b/ojluni/src/main/java/java/net/SocketImpl.java
@@ -222,7 +222,14 @@
      * @return  the value of this socket's <code>fd</code> field.
      * @see     java.net.SocketImpl#fd
      */
-    public FileDescriptor getFileDescriptor() {
+    protected FileDescriptor getFileDescriptor() {
+        return fd;
+    }
+
+    /**
+     * @hide used by java.nio tests
+     */
+    public FileDescriptor getFD$() {
         return fd;
     }