- Restructure plugin module using a "module struct" rather than global variables.

This include plugin module init and exit functions
  New type: clixon_plugin_t exposed via public API while struct clixon_plugin is private
- Makefile changes for static linkage using "LINKAGE=static"
- Moved nacm external init to later stage in backend_main

apps/netconf/netconf_main.c

@@ -584,8 +584,9 @@ netconf_terminate(clicon_handle h)
     cvec       *nsctx;
     cxobj      *x;
     
-    clixon_plugin_exit_all(h);
-    rpc_callback_delete_all(h);
+    /* Delete all plugins, and RPC callbacks */
+    clixon_plugin_module_exit(h);
+
     clicon_rpc_close_session(h);
     if ((yspec = clicon_dbspec_yang(h)) != NULL)
 	ys_free(yspec);
@@ -796,6 +797,10 @@ main(int    argc,
     if (netconf_module_features(h) < 0)
 	goto done;
     
+    /* Initialize plugin module by creating a handle holding plugin and callback lists */
+    if (clixon_plugin_module_init(h) < 0)
+	goto done;
+    
     /* Create top-level yang spec and store as option */
     if ((yspec = yspec_new()) == NULL)
 	goto done;