LU-5650 mgc: check the import stat for lprocfs

LU-5650 mgc: check the import stat for lprocfs

in lprocfs_mgc_rd_ir_state, the import state should be checked
the validity before doing further work.

This patch is back-ported from the following one:
Lustre-commit: 4295402585605e1ba210ad96c12e3820fa523f7b
Lustre-change: http://review.whamcloud.com/12327

Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Change-Id: I41a5f7547d24bf61ce83dd488aef699409be209b
Reviewed-on: http://review.whamcloud.com/12896
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>