ipcs: fix shmctl() usage

ipcs: fix shmctl() usage

The function shmctl() has to be called with 'struct shmid_ds', and if
you need 'struct shminfo' then the right way is to cast:

bad way:
  struct shm_info info;

  shmctl(0, SHM_INFO, &info);

right way:
  struct shmid_ds buf;
  struct shm_info *info;

  shmctl(0, SHM_INFO, &buf);
  info = (struct shm_info *) &buf);

The patch also fixes bug in ipc_shm_get_limits() where is missing
lim->shmmax in code based on shmctl().

Signed-off-by: Karel Zak <kzak@redhat.com>