Minor changes to the async DNS query API flag definitions.

1. Use JavaDoc style comments instead of // comments.
2. Change the flags from an enum class to a uint32_t.

Test: built, flashed, booted
      cts test: NativeDnsAsyncTest

Change-Id: I897916a22f19fec6dc70592de590f425d2fe92de
diff --git a/include/android/multinetwork.h b/include/android/multinetwork.h
index 05d96ff..d31d1f1 100644
--- a/include/android/multinetwork.h
+++ b/include/android/multinetwork.h
@@ -112,15 +112,25 @@
 
 #if __ANDROID_API__ >= 29
 
+/**
+ * Possible values of the flags argument to android_res_nsend and android_res_nquery.
+ * Values are ORed together.
+ */
 enum ResNsendFlags : uint32_t {
-    // Send a single request to a single resolver and fail on timeout or network errors
+    /**
+     * Send a single request to a single resolver and fail on timeout or network errors
+     */
     ANDROID_RESOLV_NO_RETRY = 1 << 0,
 
-    // Do not cache the result of the lookup. The lookup may return a result that is already
-    // in the cache, unless the ANDROID_RESOLV_NO_CACHE_LOOKUP flag is also specified.
+    /**
+     * Do not cache the result of the lookup. The lookup may return a result that is already
+     * in the cache, unless the ANDROID_RESOLV_NO_CACHE_LOOKUP flag is also specified.
+     */
     ANDROID_RESOLV_NO_CACHE_STORE = 1 << 1,
 
-    // Don't lookup the request in cache, do not write back the response into the cache
+    /**
+     * Don't lookup the request in cache.
+     */
     ANDROID_RESOLV_NO_CACHE_LOOKUP = 1 << 2,
 };
 
@@ -136,8 +146,7 @@
  * POSIX error code (see errno.h) if an immediate error occurs.
  */
 int android_res_nquery(net_handle_t network,
-        const char *dname, int ns_class, int ns_type,
-        enum ResNsendFlags flags) __INTRODUCED_IN(29);
+        const char *dname, int ns_class, int ns_type, uint32_t flags) __INTRODUCED_IN(29);
 
 /**
  * Issue the query |msg| on the given |network|.
@@ -148,10 +157,11 @@
  * POSIX error code (see errno.h) if an immediate error occurs.
  */
 int android_res_nsend(net_handle_t network,
-        const uint8_t *msg, size_t msglen, enum ResNsendFlags flags) __INTRODUCED_IN(29);
+        const uint8_t *msg, size_t msglen, uint32_t flags) __INTRODUCED_IN(29);
 
 /**
  * Read a result for the query associated with the |fd| descriptor.
+ * Closes |fd| before returning.
  *
  * Returns:
  *     < 0: negative POSIX error code (see errno.h for possible values). |rcode| is not set.