Add unit test for shared/unshared interface quotas

Test: as follows
    - built
    - flashed
    - booted
    - "runtest -x .../netd_unit_test.cpp" passes
Bug: 28362720
Bug: 38143143

Change-Id: I0b962898f9e3d7e86d5c0d0d01b79b3e3543b5ee
diff --git a/libnetdutils/Android.bp b/libnetdutils/Android.bp
index c2f97ab..fd8c89f 100644
--- a/libnetdutils/Android.bp
+++ b/libnetdutils/Android.bp
@@ -9,6 +9,7 @@
         "Status.cpp",
         "Syscalls.cpp",
         "UniqueFd.cpp",
+        "UniqueFile.cpp",
     ],
     shared_libs: [
         "libbase",