Add ICMPv6 NS Souce Link Layer Option Length constant

Bug: 337807604
Test: TH
Change-Id: Iaef51d344fa727e43edde307b0f07cd31bea7701
diff --git a/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
index 19d8bbe..319d51a 100644
--- a/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
+++ b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
@@ -180,6 +180,7 @@
     public static final int ICMPV6_NS_HEADER_LEN = 24;
     public static final int ICMPV6_NA_HEADER_LEN = 24;
     public static final int ICMPV6_ND_OPTION_TLLA_LEN = 8;
+    public static final int ICMPV6_ND_OPTION_SLLA_LEN = 8;
 
     public static final int NEIGHBOR_ADVERTISEMENT_FLAG_ROUTER    = 1 << 31;
     public static final int NEIGHBOR_ADVERTISEMENT_FLAG_SOLICITED = 1 << 30;