Add method to get socket cookie from socket FileDescriptor

aosp/3502915 use this method from ConnectivityService to get socket
cookie that is required for closing QUIC connection.

Bug: 311792075
Test: m, boot
Change-Id: I17d8a4dd24cfb84e9b008b8eb87eedec67b29020

framework/src/android/net/NetworkUtils.java

@@ -443,4 +443,13 @@ public class NetworkUtils {
 
     /** Returns whether the Linux Kernel is x86 */
     public static native boolean isKernelX86();
+
+    /**
+     * Returns socket cookie.
+     *
+     * @param fd The socket file descriptor
+     * @return The socket cookie.
+     * @throws ErrnoException if retrieving the socket cookie fails.
+     */
+    public static native long getSocketCookie(FileDescriptor fd) throws ErrnoException;
 }