LU-8585 llite: add special fid handling for fhandle API

LU-8585 llite: add special fid handling for fhandle API

Lustre has been moving its FIDs handling to the fhandle API. This
works well for normal files but Lustre has special FIDs that don't
map to normal files which are used by user land applications. Add
special handling to ll_iget_for_nfs() so the fhandle API can work
with these special FIDs. These FIDs should also work with filesets.

Change-Id: I4b55d96cc9eea0b1fb898f94c071c8b30c7b2bd5
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51707
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Etienne AUJAMES <eaujames@ddn.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>