Add NDK API for getprocdns,setprocdns

The API allows callers to control the default network that is used for
DNS hostname resolution.

Test: atest CtsNetTestCases
      Tests in change I00143cafcd3eb1d71e8d5c7ea9c839a99dc6f4ce
Bug: 171540887
Change-Id: I42f0d9b17b3058f6e10fd2e651278b290f26667f

native/android/libandroid.map.txt

@@ -287,6 +287,8 @@ LIBANDROID {
     android_getaddrinfofornetwork; # introduced=23
     android_getprocnetwork; # introduced=31
     android_setprocnetwork; # introduced=23
+    android_getprocdns; # introduced=31
+    android_setprocdns; # introduced=31
     android_setsocknetwork; # introduced=23
     android_res_cancel; # introduced=29
     android_res_nquery; # introduced=29

native/android/libandroid_net.map.txt

@@ -16,6 +16,8 @@ LIBANDROID_NET {
     android_res_nsend; # llndk
     # These functions have been part of the NDK since API 31.
     android_getprocnetwork; # llndk
+    android_setprocdns; # llndk
+    android_getprocdns; # llndk
   local:
     *;
 };

native/android/net.c

@@ -90,6 +90,38 @@ int android_getprocnetwork(net_handle_t *network) {
     return 0;
 }
 
+int android_setprocdns(net_handle_t network) {
+    unsigned netid;
+    if (!getnetidfromhandle(network, &netid)) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    int rval = setNetworkForResolv(netid);
+    if (rval < 0) {
+        errno = -rval;
+        rval = -1;
+    }
+    return rval;
+}
+
+int android_getprocdns(net_handle_t *network) {
+    if (network == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    unsigned netid;
+    int rval = getNetworkForDns(&netid);
+    if (rval < 0) {
+        errno = -rval;
+        return -1;
+    }
+
+    *network = gethandlefromnetid(netid);
+    return 0;
+}
+
 int android_getaddrinfofornetwork(net_handle_t network,
         const char *node, const char *service,
         const struct addrinfo *hints, struct addrinfo **res) {