- pim_protocol warning fix

- ipmr_vif_open() and ipmr_mfc_open() allocates the memory, so it
  should use seq_release_private().

- ipmr_mfc_seq_xxx is using it->cache, in order to control whether
  unlock should be do or not, but it->cache was not initialized in
  ipmr_mfc_seq_start(). So it can point the previous state if user
  did seek(). This become to the cause of twice unlock.
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: David S. Miller <davem@redhat.com>