Move resolver public headers to separate include path

Additionally rename functions and structs to eliminate those ugly
underscores from the public API (with the notable exception of
__res_params, which will come in its own separate change to keep this
one from growing too large).

Test: build, flash, then 'atest netd_integration_test'
Change-Id: I7e9b0ee6cdbec889e9c35b5a17b5daa65533686e
diff --git a/client/NetdClient.cpp b/client/NetdClient.cpp
index 3fd985e..c4e7e2f 100644
--- a/client/NetdClient.cpp
+++ b/client/NetdClient.cpp
@@ -27,8 +27,8 @@
 #include "Fwmark.h"
 #include "FwmarkClient.h"
 #include "FwmarkCommand.h"
-#include "resolv_netid.h"
 #include "Stopwatch.h"
+#include "netid_client.h"
 
 namespace {