NetworkStackConstants: add ICMP checksum offset constant

Bug: 237369591
Test: NetworkStaticLibTests
Change-Id: I7175c9ae3c547639fcfe2e252dad591ad2c3ec8a
diff --git a/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
index 1ad9c35..ebef155 100644
--- a/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
+++ b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
@@ -127,6 +127,14 @@
             (Inet6Address) InetAddresses.parseNumericAddress("ff02::3");
 
     /**
+     * ICMP constants.
+     *
+     * See also:
+     *     - https://tools.ietf.org/html/rfc792
+     */
+    public static final int ICMP_CHECKSUM_OFFSET = 2;
+
+    /**
      * ICMPv6 constants.
      *
      * See also: