LU-7613 llite: changes to avoid cache corruption

LU-7613 llite: changes to avoid cache corruption

ll_find_alias is responsible for getting alias for inode
which can be reused. Directories are assumed to have unique
alias, where in case of non-directories there can be multiple
aliases. In case of lustre there can be two type of aliases
i.e. discon_alias and invalid_alias. Usage of discon_alias in
case of non-directories may corrupt dcache and leads to kernel
crash. Changes made to avoid use of discon_alias in case of
non-directories.

Seagate-bug-id: MRP-2739, MRP-3601
Change-Id: Ieb9dabab0784bdb3c52e2cb32be1a766ffe55313
Signed-off-by: Lokesh Nagappa Jaliminche <lokesh.jaliminche@seagate.com>
Reviewed-by: Ujjwal Lanjewar <ujjwal.lanjewar@seagate.com>
Reviewed-by: Ashish Purkar <ashish.purkar@seagate.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Tested-by: Parinay Vijayprakash Kondekar <parinay.kondekar@seagate.com>
Reviewed-on: http://review.whamcloud.com/17732
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>