Add NDK API for getprocnetwork

The API is the getter couterpart for setprocnetwork.
Use it in NetworkUtils so that the NDK API can be the source of truth
for the process network.

Bug: 171540887
Test: atest CtsNetTestCases
      Tests in change I311b58585033c2ca50ce5477ea9cd94b6f127507
Merged-In: Ie8f68cf1fa57deddb63324c1abf3d6fd5b0ef500
Change-Id: If37c1480e8a6fe22ce0340858fcde052e8770923
diff --git a/native/android/libandroid_net.map.txt b/native/android/libandroid_net.map.txt
index 8d4e900..cc8dd72 100644
--- a/native/android/libandroid_net.map.txt
+++ b/native/android/libandroid_net.map.txt
@@ -14,6 +14,8 @@
     android_res_nquery; # llndk
     android_res_nresult; # llndk
     android_res_nsend; # llndk
+    # These functions have been part of the NDK since API 31.
+    android_getprocnetwork; # llndk
   local:
     *;
 };