LU-14185 osp: alloc fails for OSP obj xattr cache

LU-14185 osp: alloc fails for OSP obj xattr cache

osp_oac_xattr_find_or_add() may get ENOMEM as it tries to allocate
over len=buf->lb_len=XATTR_SIZE_MAX, thus order:5. Use large alloc
instead.

HPE-bug-id: LUS-9551
Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: I98c08d16d0343cb60f6efcb63d20739103f2af1c
Reviewed-by: Sergey Cheremencev <c17829@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Tested-by: Alexander Lezhoev <c17454@cray.com>
Reviewed-on: https://review.whamcloud.com/40871
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>