Add the DNS query hook to net context

This change
 - adds a query hook to android_net_context
 - exposes relevant definitions to netd
 - corrects a bug in query hooks' interaction with the cache

This change does not introduce any code to read the query hook
from the net context or make use of it.

Bug: 34953048
Test: Netd test suite passes
Change-Id: Ie091980e22ce9da07a3c4d387b371e544379d762
diff --git a/libc/dns/include/resolv_netid.h b/libc/dns/include/resolv_netid.h
index 37c1891..ae94768 100644
--- a/libc/dns/include/resolv_netid.h
+++ b/libc/dns/include/resolv_netid.h
@@ -34,6 +34,7 @@
  */
 #include <sys/cdefs.h>
 #include <netinet/in.h>
+#include "resolv_params.h"
 #include <stdio.h>
 
 /*
@@ -71,6 +72,7 @@
     unsigned dns_netid;
     unsigned dns_mark;
     uid_t uid;
+    res_send_qhook qhook;
 };
 
 #define NET_CONTEXT_INVALID_UID ((uid_t)-1)