global: Add or update copyright headers in Java code

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/src/main/java/com/wireguard/config/Attribute.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright © 2018 Samuel Holland <samuel@sholland.org>
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
 package com.wireguard.config;
 
 import android.text.TextUtils;

app/src/main/java/com/wireguard/config/Config.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright © 2018 Samuel Holland <samuel@sholland.org>
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
 package com.wireguard.config;
 
 import android.databinding.BaseObservable;

app/src/main/java/com/wireguard/config/IPCidr.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright © 2018 Samuel Holland <samuel@sholland.org>
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
 package com.wireguard.config;
 
 import java.net.Inet4Address;

app/src/main/java/com/wireguard/config/Interface.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright © 2018 Samuel Holland <samuel@sholland.org>
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
 package com.wireguard.config;
 
 import android.databinding.BaseObservable;

app/src/main/java/com/wireguard/config/Peer.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright © 2018 Samuel Holland <samuel@sholland.org>
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
 package com.wireguard.config;
 
 import android.databinding.BaseObservable;