tunnel: add javadoc support

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tunnel/src/main/java/com/wireguard/android/backend/Tunnel.java

@@ -33,7 +33,6 @@ public interface Tunnel {
      * React to a change in state of the tunnel. Should only be directly called by Backend.
      *
      * @param newState The new state of the tunnel.
-     * @return The new state of the tunnel.
      */
     void onStateChange(State newState);
 

tunnel/src/main/java/com/wireguard/crypto/Curve25519.java

@@ -28,7 +28,7 @@ import androidx.annotation.Nullable;
  */
 @SuppressWarnings({"MagicNumber", "NonConstantFieldWithUpperCaseName", "SuspiciousNameCombination"})
 @NonNullForAll
-public final class Curve25519 {
+final class Curve25519 {
     // Numbers modulo 2^255 - 19 are broken up into ten 26-bit words.
     private static final int NUM_LIMBS_255BIT = 10;
     private static final int NUM_LIMBS_510BIT = 20;

tunnel/src/main/java/com/wireguard/util/NonNullForAll.java

@@ -5,7 +5,6 @@
 
 package com.wireguard.util;
 
-import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -13,12 +12,15 @@ import java.lang.annotation.RetentionPolicy;
 import javax.annotation.Nonnull;
 import javax.annotation.meta.TypeQualifierDefault;
 
+import androidx.annotation.RestrictTo;
+import androidx.annotation.RestrictTo.Scope;
+
 /**
  * This annotation can be applied to a package, class or method to indicate that all
  * class fields and method parameters and return values in that element are nonnull
  * by default unless overridden.
  */
-@Documented
+@RestrictTo(Scope.LIBRARY_GROUP)
 @Nonnull
 @TypeQualifierDefault({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
 @Retention(RetentionPolicy.RUNTIME)