dns cache per interface iteration 2

name server addresses are read from the dns
cache associated wih the interface on which
the request shall be done.

processes which has requested to issue dns request
using specific interface are now proxied to netd.

added methods to attach/detach a process to a specific
dns cache/interface.

added getaddrinfoforinface method which takes an
interface as an argument.

bug:4815099
bug:5465296
Change-Id: I7a8fe1980cdf99d4d296ddc5c6411f0c72162263

libc/netbsd/resolv/res_data.c

@@ -82,13 +82,7 @@ extern struct __res_state _nres;
 
 int  res_ourserver_p(const res_state, const struct sockaddr *);
 
-#ifdef ANDROID_CHANGES
-static int res_need_init() {
-	return ((_nres.options & RES_INIT) == 0U) || res_get_dns_changed();
-}
-#else
 #define res_need_init()   ((_nres.options & RES_INIT) == 0U)
-#endif
 
 int
 res_init(void) {