EX-4567 kernel: add extra field for snapshot in el8

EX-4567 kernel: add extra field for snapshot in el8

Adding extra fields in "struct jbd2_journal_handle" and
"struct journal_head", which are used by snapshot into the
4-byte hole at the end of struct jbd2_journal_handle so
that they do not increase the structure size and memory
usage for this common allocation.

Use RH_KABI_EXTEND() and RH_KABI_FILL_HOLE() so that the
new fields do not affect the kernel ABI compatibility.

Change-Id: I84f52b18694e56d837d64c5c80076e45dde27eab
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48880
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>