plugin: Add PRE_DUMP stage into plugins

It is missged in first place and may cause
problem on exiting via alarm hanling.
Reported-by: Igor Sukhih <igor@virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

cr-dump.c

@@ -1466,6 +1466,9 @@ int cr_pre_dump_tasks(pid_t pid)
 	if (init_stats(DUMP_STATS))
 		goto err;
 
+	if (cr_plugin_init(CR_PLUGIN_STAGE__PRE_DUMP))
+		goto err;
+
 	if (kerndat_init())
 		goto err;
 

include/criu-plugin.h

@@ -66,6 +66,7 @@ DECLARE_PLUGIN_HOOK_ARGS(CR_PLUGIN_HOOK__DUMP_EXT_LINK, int index, int type, cha
 
 enum {
 	CR_PLUGIN_STAGE__DUMP,
+	CR_PLUGIN_STAGE__PRE_DUMP,
 	CR_PLUGIN_STAGE__RESTORE,
 
 	CR_PLUGIN_STAGE_MAX