Add logic to retrieve KS2 certificates in supplicant.

Logic was largely copied from
android.system.wifi.keystore@1.0

Bug: 205764502
Test: Manual test - store a key-value pair to
      legacy Keystore. Check that we can retrieve
      the value in supplicant using the new method.
Change-Id: I8f12e447747f2e1a98e2d37b3453526cdde9e2de
diff --git a/wpa_supplicant/Android.bp b/wpa_supplicant/Android.bp
index 05c79c0..7db0ef3 100644
--- a/wpa_supplicant/Android.bp
+++ b/wpa_supplicant/Android.bp
@@ -68,6 +68,7 @@
     srcs: [":wpa_supplicant_srcs"],
     shared_libs: [
         "android.hardware.wifi.supplicant-V2-ndk",
+        "android.system.keystore2-V1-ndk",
         "libbase",
         "libbinder_ndk",
         "libc",