Make private final field static

It's used as a constant.

Change-Id: Ic267e8cb5b62228de15e134cd80725df592a0171

org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackOutputStream.java

@@ -56,7 +56,7 @@ import org.eclipse.jgit.util.NB;
 
 /** Custom output stream to support {@link PackWriter}. */
 public final class PackOutputStream extends OutputStream {
-	private final int BYTES_TO_WRITE_BEFORE_CANCEL_CHECK = 128 * 1024;
+	private static final int BYTES_TO_WRITE_BEFORE_CANCEL_CHECK = 128 * 1024;
 
 	private final ProgressMonitor writeMonitor;