REORG: server: attach servers in parse_server

Move server linked into proxy backend list outside of _srv_parse_init to
parse_server.

This is groundwork for dynamic servers support. There will be two
differences in case of a dynamic server :
- the server will be attached to the proxy list only at the very end of the
  operations when everything is ok
- the server will be directly attached to the end of the server proxy
  list
diff --git a/src/server.c b/src/server.c
index 3fa3845..cbeae85 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2405,9 +2405,6 @@
 				newsrv->tmpl_info.nb_high = tmpl_range_high;
 			}
 
-			/* the servers are linked backwards first */
-			newsrv->next = curproxy->srv;
-			curproxy->srv = newsrv;
 			/* Note: for a server template, its id is its prefix.
 			 * This is a temporary id which will be used for server allocations to come
 			 * after parsing.
@@ -2648,6 +2645,12 @@
 			free(errmsg);
 		}
 
+		/* the servers are linked backwards first */
+		if (newsrv && !defsrv) {
+			newsrv->next = curproxy->srv;
+			curproxy->srv = newsrv;
+		}
+
 		if (err_code & ERR_CODE)
 			goto out;
 
@@ -2683,6 +2686,7 @@
 		if (srv_tmpl)
 			_srv_parse_tmpl_init(newsrv, curproxy);
 	}
+
 	return 0;
 
  out: