Modules compatibility: down flag promoted to a bitmask.

It is to be used as a bitmask with various bits set/reset when appropriate.
Any bit set means that the peer should not be used, that is, exactly what
current checks do, no additional changes required.

src/http/ngx_http_upstream_round_robin.h

diff --git a/src/http/ngx_http_upstream_round_robin.h b/src/http/ngx_http_upstream_round_robin.h
index 6323abf..326e849 100644
--- a/src/http/ngx_http_upstream_round_robin.h
+++ b/src/http/ngx_http_upstream_round_robin.h
@@ -38,7 +38,7 @@
     ngx_msec_t                      slow_start;
     ngx_msec_t                      start_time;
 
-    ngx_uint_t                      down;          /* unsigned  down:1; */
+    ngx_uint_t                      down;
 
 #if (NGX_HTTP_SSL)
     void                           *ssl_session;

src/stream/ngx_stream_upstream_round_robin.h

diff --git a/src/stream/ngx_stream_upstream_round_robin.h b/src/stream/ngx_stream_upstream_round_robin.h
index 9540c12..75ffadd 100644
--- a/src/stream/ngx_stream_upstream_round_robin.h
+++ b/src/stream/ngx_stream_upstream_round_robin.h
@@ -38,7 +38,7 @@
     ngx_msec_t                       slow_start;
     ngx_msec_t                       start_time;
 
-    ngx_uint_t                       down;         /* unsigned  down:1; */
+    ngx_uint_t                       down;
 
 #if (NGX_STREAM_SSL)
     void                            *ssl_session;