staging/lustre/lfsck: LFSCK 1.5 technical debts (3)

Original patch resolves some LFSCK 1.5 technical debts, including:
1) Check and remove repeated linkea entries.
2) Merge some "goto" branches to make the code more readable.
3) Some comments about object's nlink inconsistency processing.

This patch picks the obd flags change.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2915
Lustre-change: http://review.whamcloud.com/6344
Signed-off-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>