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/resolv/res_send.c b/libc/dns/resolv/res_send.c
index f53da5f..71cc852 100644
--- a/libc/dns/resolv/res_send.c
+++ b/libc/dns/resolv/res_send.c
@@ -523,6 +523,10 @@
 					res_nclose(statp);
 					goto next_ns;
 				case res_done:
+					if (cache_status == RESOLV_CACHE_NOTFOUND) {
+						_resolv_cache_add(statp->netid, buf, buflen,
+								ans, resplen);
+					}
 					return (resplen);
 				case res_modified:
 					/* give the hook another try */