Fix breaking changes.

MQTTnet.Core/Packets/MqttConnAckPacket.cs

@@ -2,7 +2,7 @@
 
 namespace MQTTnet.Core.Packets
 {
-    public class MqttConnAckPacket : MqttBasePacket
+    public sealed class MqttConnAckPacket : MqttBasePacket
     {
         public bool IsSessionPresent { get; set; }
 

MQTTnet.Core/Packets/MqttConnectPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttConnectPacket: MqttBasePacket
+    public sealed class MqttConnectPacket: MqttBasePacket
     {
         public string ClientId { get; set; }
 

MQTTnet.Core/Packets/MqttDisconnectPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttDisconnectPacket : MqttBasePacket
+    public sealed class MqttDisconnectPacket : MqttBasePacket
     {
     }
 }

MQTTnet.Core/Packets/MqttPingReqPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPingReqPacket : MqttBasePacket
+    public sealed class MqttPingReqPacket : MqttBasePacket
     {
         public override string ToString()
         {

MQTTnet.Core/Packets/MqttPingRespPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPingRespPacket : MqttBasePacket
+    public sealed class MqttPingRespPacket : MqttBasePacket
     {
         public override string ToString()
         {

MQTTnet.Core/Packets/MqttPubAckPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPubAckPacket : MqttBasePublishPacket
+    public sealed class MqttPubAckPacket : MqttBasePublishPacket
     {
     }
 }

MQTTnet.Core/Packets/MqttPubCompPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPubCompPacket : MqttBasePublishPacket
+    public sealed class MqttPubCompPacket : MqttBasePublishPacket
     {
     }
 }

MQTTnet.Core/Packets/MqttPubRecPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPubRecPacket : MqttBasePublishPacket
+    public sealed class MqttPubRecPacket : MqttBasePublishPacket
     {
     }
 }

MQTTnet.Core/Packets/MqttPubRelPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPubRelPacket : MqttBasePublishPacket
+    public sealed class MqttPubRelPacket : MqttBasePublishPacket
     {
     }
 }

MQTTnet.Core/Packets/MqttPublishPacket.cs

@@ -3,7 +3,7 @@ using MQTTnet.Core.Protocol;
 
 namespace MQTTnet.Core.Packets
 {
-    public class MqttPublishPacket : MqttBasePublishPacket
+    public sealed class MqttPublishPacket : MqttBasePublishPacket
     {
         public bool Retain { get; set; }
 

MQTTnet.Core/Packets/MqttSubAckPacket.cs

@@ -4,7 +4,7 @@ using MQTTnet.Core.Protocol;
 
 namespace MQTTnet.Core.Packets
 {
-    public class MqttSubAckPacket : MqttBasePacket, IPacketWithIdentifier
+    public sealed class MqttSubAckPacket : MqttBasePacket, IPacketWithIdentifier
     {
         public ushort PacketIdentifier { get; set; }
 

MQTTnet.Core/Packets/MqttSubscribePacket.cs

@@ -3,7 +3,7 @@ using System.Linq;
 
 namespace MQTTnet.Core.Packets
 {
-    public class MqttSubscribePacket : MqttBasePacket, IPacketWithIdentifier
+    public sealed class MqttSubscribePacket : MqttBasePacket, IPacketWithIdentifier
     {
         public ushort PacketIdentifier { get; set; }
         

MQTTnet.Core/Packets/MqttUnsubAckPacket.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Core.Packets
 {
-    public class MqttUnsubAckPacket : MqttBasePacket, IPacketWithIdentifier
+    public sealed class MqttUnsubAckPacket : MqttBasePacket, IPacketWithIdentifier
     {
         public ushort PacketIdentifier { get; set; }
     }

MQTTnet.Core/Packets/MqttUnsubscribe.cs

@@ -2,7 +2,7 @@
 
 namespace MQTTnet.Core.Packets
 {
-    public class MqttUnsubscribePacket : MqttBasePacket, IPacketWithIdentifier
+    public sealed class MqttUnsubscribePacket : MqttBasePacket, IPacketWithIdentifier
     {
         public ushort PacketIdentifier { get; set; }
         

MQTTnet.Core/Packets/TopicFilter.cs

@@ -2,7 +2,7 @@
 
 namespace MQTTnet.Core.Packets
 {
-    public class TopicFilter
+    public sealed class TopicFilter
     {
         public TopicFilter(string topic, MqttQualityOfServiceLevel qualityOfServiceLevel)
         {