Separate Struct.java into its own lib.

* Struct.java is removed from net-utils-device-common-bpf and
  net-utils-device-common-struct's source list
* Created a lib net-utils-device-common-struct-base for Struct.java
* Updated libs that require Struct.java to include
  net-utils-device-common-struct-base.
* Replaced net-utils-multicast-forwarding-structs with
  net-utils-device-common-struct in service-connectivity

Bug: 323503345

Test: build tethering module.
Change-Id: I3f60715c3d8043b7569db7612dee9d4fa1ccba59

thread/service/Android.bp

@@ -45,6 +45,9 @@ java_library {
         "modules-utils-shell-command-handler",
         "net-utils-device-common",
         "net-utils-device-common-netlink",
+        // The required dependency net-utils-device-common-struct-base is in the classpath via
+        // framework-connectivity
+        "net-utils-device-common-struct",
         "ot-daemon-aidl-java",
     ],
     apex_available: ["com.android.tethering"],

thread/tests/integration/Android.bp

@@ -30,6 +30,7 @@ java_defaults {
         "net-tests-utils",
         "net-utils-device-common",
         "net-utils-device-common-bpf",
+        "net-utils-device-common-struct-base",
         "testables",
         "ThreadNetworkTestUtils",
         "truth",

thread/tests/utils/Android.bp

@@ -27,6 +27,7 @@ java_library {
         "net-tests-utils",
         "net-utils-device-common",
         "net-utils-device-common-bpf",
+        "net-utils-device-common-struct-base",
     ],
     srcs: [
         "src/**/*.java",