Use <resolv_iface.h> instead of <resolv.h>

The declarations for _resolv_set_default_iface() and others were
initially added to a public C library header (<resolv.h>). This was a
mistake and they have been moved to a private header
(bionic/libc/private/resolv_iface.h)

This patch updates netd to use the correct private header.

Change-Id: I186390ea3675685b4e0dd5b8a099bd21911f059e
diff --git a/ResolverController.cpp b/ResolverController.cpp
index 3e3cc0d..680be20 100644
--- a/ResolverController.cpp
+++ b/ResolverController.cpp
@@ -20,7 +20,10 @@
 #include <cutils/log.h>
 
 #include <linux/if.h>
-#include <resolv.h>
+
+// NOTE: <resolv_iface.h> is a private C library header that provides
+//       declarations for _resolv_set_default_iface() and others.
+#include <resolv_iface.h>
 
 #include "ResolverController.h"