Refactored heavily #ifdefd capability code to its own libstrongswan class

src/charon-nm/nm/nm_backend.c

@@ -137,7 +137,7 @@ static bool nm_backend_init()
 	}
 
 	/* bypass file permissions to read from users ssh-agent */
-	charon->keep_cap(charon, CAP_DAC_OVERRIDE);
+	charon->caps->keep(charon->caps, CAP_DAC_OVERRIDE);
 
 	lib->processor->queue_job(lib->processor,
 		(job_t*)callback_job_create_with_prio((callback_job_cb_t)run, this,
@@ -171,4 +171,4 @@ void nm_backend_register()
 	};
 	lib->plugins->add_static_features(lib->plugins, "nm-backend", features,
 									  countof(features), TRUE);
-}
+}