MFC 1.3: Check if the filedes of kevent is expected one.

Though our old resolver opened just one socket, BIND9's
resolver may open more than one sockets.  And, BIND9's
resolver doesn't close the socket on timeout.  So, we
need this check.

lib/libc/resolv/res_send.c

@@ -970,6 +970,10 @@ send_dg(res_state statp,
 		res_nclose(statp);
 		return (0);
 	}
+#ifdef USE_KQUEUE
+	if (kv.ident != s)
+		goto wait;
+#endif
 	errno = 0;
 	fromlen = sizeof(from);
 	resplen = _recvfrom(s, (char*)ans, anssiz,0,