Add @Keep annotation to Player constructor

Since it's only instantiated from c++.

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/features/netplay/model/Player.kt

@@ -2,6 +2,9 @@
 
 package org.dolphinemu.dolphinemu.features.netplay.model
 
+import androidx.annotation.Keep
+
+@Keep
 data class Player(
     val pid: Int,
     val name: String,