bionic: Replace iface with opaque netid in resolver.

Replace iface cache key with netid.

Replace _mark with netid.

Mark sockets used to test IPv4/IPv6 support as well as sockets
used to determine source address for rfc6724 sort.

Remove pid/uid mappings (functionality moved to system/netd).

Do not create resolv_cache when it does not exist, but rather only
when DNS configuration is supplied.

Clean up unused functions.

Change-Id: I9ccfda2902cc0943e87c9bc346ad9a2578accdab

libc/dns/resolv/res_query.c

@@ -91,6 +91,7 @@ __RCSID("$NetBSD: res_query.c,v 1.7 2006/01/24 17:41:25 christos Exp $");
 #include <errno.h>
 #include <netdb.h>
 #ifdef ANDROID_CHANGES
+#include "resolv_cache.h"
 #include "resolv_private.h"
 #else
 #include <resolv.h>
@@ -272,14 +273,14 @@ res_nsearch(res_state statp,
 	    (dots && !trailing_dot && (statp->options & RES_DNSRCH) != 0U)) {
 		int done = 0;
 
-		/* Unfortunately we need to load interface info
+		/* Unfortunately we need to load network-specific info
 		 * (dns servers, search domains) before
 		 * the domain stuff is tried.  Will have a better
 		 * fix after thread pools are used as this will
 		 * be loaded once for the thread instead of each
 		 * time a query is tried.
 		 */
-		_resolv_populate_res_for_iface(statp);
+		_resolv_populate_res_for_net(statp);
 
 		for (domain = (const char * const *)statp->dnsrch;
 		     *domain && !done;