EX-1428 kernel: contain update related to snapshot

EX-1428 kernel: contain update related to snapshot

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.

Test-Parameters: trivial
Change-Id: I6bab8ae1cfcab39632cb1397ffd7991f72e00fb4
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/41882
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>