Add support for reading unsigned short "u".

Add support for reading unsigned short "u".

https://www.rabbitmq.com/amqp-0-9-1-errata.html#section_3
(cherry picked from commit 7812ebf)

Author: gustf

src/main/java/com/rabbitmq/client/impl/ValueReader.java

@@ -194,6 +194,9 @@ static Object readFieldValue(DataInputStream in)
           case 's':
               value = in.readShort();
               break;
+          case 'u':
+              value = in.readUnsignedShort();
+              break;
           case 't':
               value = in.readBoolean();
               break;