Update Netty to 4.1.51

Minecraft's Netty version was severely out of date. There has been
numerous security fixes, bug fixes, and likely performance fixes
since the version Minecraft uses (4.1.25).

This fixes some known issues with "Closed Channel" spam.

Fixes #3388

Spigot-Server-Patches/POM-Changes.patch

@@ -64,6 +64,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +            <groupId>co.aikar</groupId>
 +            <artifactId>cleaner</artifactId>
 +            <version>1.0-SNAPSHOT</version>
++        </dependency>
++        <dependency>
++            <groupId>io.netty</groupId>
++            <artifactId>netty-all</artifactId>
++            <version>4.1.51.Final-SNAPSHOT</version>
 +        </dependency>
          <!-- deprecated API depend -->
          <dependency>
@@ -142,6 +147,20 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
                              <createSourcesJar>${shadeSourcesJar}</createSourcesJar>
                              <filters>
                                  <filter>
+@@ -0,0 +0,0 @@
+                                         <exclude>com/google/common/**</exclude>
+                                         <exclude>com/google/gson/**</exclude>
+                                         <exclude>com/google/thirdparty/**</exclude>
++                                        <!-- paper -->
++                                        <exclude>io/netty/**</exclude>
++                                        <exclude>com/brigadier/**</exclude>
++                                        <exclude>META-INF/MANIFEST.MF</exclude>
++                                        <exclude>com.mojang.authlib.yggdrasil.YggdrasilGameProfileRepository</exclude>
++                                        <exclude>com.mojang.datafixers.util.Either</exclude>
++                                        <exclude>org.apache.logging.log4j/**</exclude>
+                                     </excludes>
+                                 </filter>
+                             </filters>
 @@ -0,0 +0,0 @@
                                      <pattern>jline</pattern>
                                      <shadedPattern>org.bukkit.craftbukkit.libs.jline</shadedPattern>