Fix NsHeader class unavailable constructor.

NsHeader class has two members, however, the public constructor has only
one parameter for target IP address, that would throw the exception when
parsing the NsHeader struct due to unavailable constructor.

Bug: 162944199
Test: atest NetworkStackTests
Change-Id: I8d0a63bc258e83be55b9ec2d34ef228cf8549c2e
diff --git a/staticlibs/device/com/android/net/module/util/structs/NsHeader.java b/staticlibs/device/com/android/net/module/util/structs/NsHeader.java
index 6e0aa50..2e8b77b 100644
--- a/staticlibs/device/com/android/net/module/util/structs/NsHeader.java
+++ b/staticlibs/device/com/android/net/module/util/structs/NsHeader.java
@@ -50,8 +50,12 @@
     @Field(order = 1, type = Type.Ipv6Address)
     public Inet6Address target;
 
-    public NsHeader(final Inet6Address target) {
-        this.reserved = 0;
+    NsHeader(int reserved, final Inet6Address target) {
+        this.reserved = reserved;
         this.target = target;
     }
+
+    public NsHeader(final Inet6Address target) {
+        this(0, target);
+    }
 }