Build connectivity JNI against libc++_static

Instead of including the whole libc++ library by linking it dynamically,
use the static version so that unused symbols can be stripped.

This allows reducing the APEX size by 1MB (3.7MB -> 2.7MB), as otherwise
libc++ is included twice for 32 and 64 bit variants.

Original change (project moved):
Ia66d795cf23d6f45997278300c103976433f7c5c

Bug: 171540887
Test: Device boots and has connectivity, size reduced

Merged-In: I3c2563d4ae4e3715d0c6270344ba8f7ef067872f
Change-Id: Ie1c5b2ea274238a226ad2d827148439fd5758bb5

framework/Android.bp

@@ -137,6 +137,7 @@ cc_library_shared {
         "jni/onload.cpp",
     ],
     shared_libs: ["libandroid"],
+    stl: "libc++_static",
     apex_available: [
         "//apex_available:platform",
         "com.android.tethering",

service/Android.bp

@@ -32,6 +32,7 @@ cc_library_shared {
         "jni/com_android_server_TestNetworkService.cpp",
         "jni/onload.cpp",
     ],
+    stl: "libc++_static",
     shared_libs: [
         "libbase",
         "liblog",