drivers/rptun: should use KRN_HEAP to intialize the carveout heap

Previous patch is not corrected:
5518135: mm/mm_heap: add nokasan flag in mm_heap_config_s structure |
https://gerrit.pt.mioffice.cn/c/vela/nuttx/+/5518135

Because rptun do not want part of the share memory is used by the
struct mm_heap_s to:
1. Save the share memory;
2. Some platfrom can't use atomic operation at the share memory,
and struct mm_heap_s contains a mutex.

Signed-off-by: Bowen Wang <wangbowen6@xiaomi.com>

drivers/rptun/rptun.c

@@ -311,6 +311,7 @@ static int rptun_init_carveout(FAR struct rptun_priv_s *priv,
     }
 
   memset(&config, 0, sizeof(config));
+  config.heap    = KRN_HEAP;
   config.name    = shmname;
   config.start   = shmbase;
   config.size    = shmlen;