6957230: CharsetEncoder.maxBytesPerChar() reports 4 for UTF-8; should be 3

Summary: changged utf-8's CharsetEncoder.maxBytesPerChar to 3
Reviewed-by: alanb

src/share/classes/sun/nio/cs/UTF_8.java

@@ -358,7 +358,7 @@ class UTF_8 extends Unicode
     private static class Encoder extends CharsetEncoder {
 
         private Encoder(Charset cs) {
-            super(cs, 1.1f, 4.0f);
+            super(cs, 1.1f, 3.0f);
         }
 
         public boolean canEncode(char c) {