Remove StructIfaddrMsg ctor VisibleForTesting annotation.

This allows other class to refer StructIfaddrMsg constructor as well,
otherwise, the default visibility is private.

Bug: 263222068
Test: atest NetworkStaticLibTests
Change-Id: If571b014ade51e3387748a4df0abcb49b59cb462
diff --git a/staticlibs/device/com/android/net/module/util/netlink/StructIfaddrMsg.java b/staticlibs/device/com/android/net/module/util/netlink/StructIfaddrMsg.java
index 2802726..f9781a7 100644
--- a/staticlibs/device/com/android/net/module/util/netlink/StructIfaddrMsg.java
+++ b/staticlibs/device/com/android/net/module/util/netlink/StructIfaddrMsg.java
@@ -18,7 +18,6 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import androidx.annotation.VisibleForTesting;
 
 import com.android.net.module.util.Struct;
 import com.android.net.module.util.Struct.Field;
@@ -50,7 +49,6 @@
     @Field(order = 4, type = Type.S32)
     public final int index;
 
-    @VisibleForTesting
     public StructIfaddrMsg(short family, short prefixLen, short flags, short scope, int index) {
         this.family = family;
         this.prefixLen = prefixLen;