Use "client_header_timeout" for all requests in a connection.

Previously, only the first request in a connection used timeout
value from the "client_header_timeout" directive while reading
header.  All subsequent requests used "keepalive_timeout" for
that.

It happened because timeout of the read event was set to the
value of "keepalive_timeout" in ngx_http_set_keepalive(), but
was not removed when the next request arrived.

src/http/ngx_http_request.c

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 3db2a43..68cb345 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -2736,8 +2736,6 @@
 
     c->data = hc;
 
-    ngx_add_timer(rev, clcf->keepalive_timeout);
-
     if (ngx_handle_read_event(rev, 0) != NGX_OK) {
         ngx_http_close_connection(c);
         return;
@@ -2753,6 +2751,10 @@
         hc->pipeline = 1;
         c->log->action = "reading client pipelined request line";
 
+        if (rev->timer_set) {
+            ngx_del_timer(rev);
+        }
+
         rev->handler = ngx_http_init_request;
         ngx_post_event(rev, &ngx_posted_events);
         return;
@@ -2872,6 +2874,8 @@
     c->idle = 1;
     ngx_reusable_connection(c, 1);
 
+    ngx_add_timer(rev, clcf->keepalive_timeout);
+
     if (rev->ready) {
         ngx_post_event(rev, &ngx_posted_events);
     }
@@ -2993,6 +2997,8 @@
     c->idle = 0;
     ngx_reusable_connection(c, 0);
 
+    ngx_del_timer(rev);
+
     ngx_http_init_request(rev);
 }