Turn TestBpfMap into a common utility class.

- Move it to frameworks/libs/net/common/testutils.
- Inherit from BpfMap, so the class can be used anywhere that
  uses a real BpfMap. For example, BpfCoordinatorTest uses
  BpfMap, not IBpfMap.

Test: atest BpfCoordinatorTest
Change-Id: I7ee65e47fa46ac6aafc831f5b1823b44267ba2a6
diff --git a/staticlibs/testutils/Android.bp b/staticlibs/testutils/Android.bp
index 2dda269..1a1328f 100644
--- a/staticlibs/testutils/Android.bp
+++ b/staticlibs/testutils/Android.bp
@@ -28,6 +28,7 @@
     ],
     libs: [
         "androidx.annotation_annotation",
+        "net-utils-device-common-bpf",  // TestBpfMap extends IBpfMap.
     ],
     static_libs: [
         "androidx.test.ext.junit",