load-tester: Start numbering IDs from 1 again

ref_get() increments the number before returning it.

Fixes: 2cbaa63295 ("load-tester: Fix race condition issuing same identity")

src/libcharon/plugins/load_tester/load_tester_config.c

@@ -937,7 +937,6 @@ load_tester_config_t *load_tester_config_create()
 		.leases = hashtable_create((hashtable_hash_t)hash,
 								   (hashtable_equals_t)equals, 256),
 		.mutex = mutex_create(MUTEX_TYPE_DEFAULT),
-		.num = 1,
 		.unique_port = UNIQUE_PORT_START,
 	);