Return correct type on retain(..)

transport-sctp/src/main/java/io/netty/channel/sctp/SctpMessage.java

@@ -135,6 +135,18 @@ public final class SctpMessage extends DefaultByteBufHolder {
         }
     }
 
+    @Override
+    public SctpMessage retain() {
+        super.retain();
+        return this;
+    }
+
+    @Override
+    public SctpMessage retain(int increment) {
+        super.retain(increment);
+        return this;
+    }
+
     @Override
     public String toString() {
         if (refCnt() == 0) {

transport-udt/src/main/java/io/netty/channel/udt/UdtMessage.java

@@ -37,4 +37,15 @@ public final class UdtMessage extends DefaultByteBufHolder {
         return new UdtMessage(data().copy());
     }
 
+    @Override
+    public UdtMessage retain() {
+        super.retain();
+        return this;
+    }
+
+    @Override
+    public UdtMessage retain(int increment) {
+        super.retain(increment);
+        return this;
+    }
 }

transport/src/main/java/io/netty/channel/socket/DatagramPacket.java

@@ -55,6 +55,18 @@ public final class DatagramPacket extends DefaultByteBufHolder {
         return new DatagramPacket(data().copy(), remoteAddress());
     }
 
+    @Override
+    public DatagramPacket retain() {
+        super.retain();
+        return this;
+    }
+
+    @Override
+    public DatagramPacket retain(int increment) {
+        super.retain(increment);
+        return this;
+    }
+
     @Override
     public String toString() {
         if (refCnt() == 0) {