Update IExtensionPoint javadoc to be correct (#8568)

fmlcore/src/main/java/net/minecraftforge/fml/IExtensionPoint.java

@@ -18,7 +18,7 @@ public interface IExtensionPoint<T extends Record>
      * The predicate tests the version from a remote instance or save for acceptability (Boolean is true for impl, false for local save)
      * and returns true if the version is compatible.
      *
-     * <p>Return {@code net.minecraftforge.impl.impl.FMLNetworkConstants#IGNORESERVERONLY} in the supplier, if you wish to be ignored
+     * <p>Return {@code net.minecraftforge.network.NetworkConstants#IGNORESERVERONLY} in the supplier, if you wish to be ignored
      * as a server side only mod.</p>
      * <p>Return true in the predicate for all values of the input string (when impl boolean is true) if you are client side,
      * and don't care about matching any potential server version.</p>
@@ -27,8 +27,8 @@ public interface IExtensionPoint<T extends Record>
      * Examples: A server only mod
      * </p>
      * <pre>{@code
-     *     registerExtensionPoint(DISPLAYTEST, ()->Pair.of(
-     *      ()->FMLNetworkConstants.IGNORESERVERONLY, // ignore me, I'm a server only mod
+     *     registerExtensionPoint(DisplayTest.class, ()->new DisplayTest(
+     *      ()->NetworkConstants.IGNORESERVERONLY, // ignore me, I'm a server only mod
      *      (s,b)->true // i accept anything from the server or the save, if I'm asked
      *     )
      * }</pre>
@@ -37,7 +37,7 @@ public interface IExtensionPoint<T extends Record>
      * Examples: A client only mod
      * </p>
      * <pre>{@code
-     *     registerExtensionPoint(DISPLAYTEST, ()->Pair.of(
+     *     registerExtensionPoint(DisplayTest.class, ()->new DisplayTest(
      *      ()->"anything. i don't care", // if i'm actually on the server, this string is sent but i'm a client only mod, so it won't be
      *      (remoteversionstring,networkbool)->networkbool // i accept anything from the server, by returning true if it's asking about the server
      *     )