Add BpfDump.toBase64EncodedString to dump raw map

Move base64 related bpf map function and constant from BpfCoordinator.
This is preparation for testing BPF map in ClatCoordinator.

Test: atest NetworkStaticLibTests
Change-Id: I3a23393abe5b108cdb8d621e99b74fd20847474e
diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index 31a7262..e5f8d58 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -111,6 +111,7 @@
     name: "net-utils-device-common-bpf",
     srcs: [
         "device/com/android/net/module/util/BpfBitmap.java",
+        "device/com/android/net/module/util/BpfDump.java",
         "device/com/android/net/module/util/BpfMap.java",
         "device/com/android/net/module/util/BpfUtils.java",
         "device/com/android/net/module/util/HexDump.java",