LU-8084 lfsck: handle linkea record length properly

The record length in the linkea may be corrupted. If we do not handle
the invalid record length when locate the next linkea record or delete
the current record, it may cause invalid memory accessing and corrupt
other data in RAM, and then cause kinds of strange RAM issues.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I27d724025c8157ecf51e3269a39e2fdfbc27a27d
Reviewed-on: http://review.whamcloud.com/19877
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>