Add libnetd_updatable to tethering-module-sdk

System libraries and binaries (e.g. netd) have a dependency on this.
Adding it to the sdk module allows an external snapshotting script
to generate prebuilts stubs of this library and commit them to
prebuilts/module_sdk. This allows minimal branch setup to build against
the apis of libnetd_updatable without checking out its source code.

Bug: 273723791
Test: m tethering-module-sdk
Change-Id: I1f235d86abba2c37ca7d750dea7071227e1346fe

Tethering/Android.bp

@@ -250,6 +250,9 @@ sdk {
         // e.g. *classpath_fragments.
         "com.android.tethering",
     ],
+    native_shared_libs: [
+        "libnetd_updatable",
+    ],
 }
 
 java_library_static {