LU-18947 osd-zfs: rename TXG_* to DMU_TX_*

LU-18947 osd-zfs: rename TXG_* to DMU_TX_*

zfs-2.3.99-237-gf69631992
  dmu_tx: rename dmu_tx_assign() flags from TXG_* to DMU_TX_*

Rename TXG_* to DMU_TX_* and provide replacements for older
releases of zfs.

HPE-bug-id: LUS-12840
Test-Parameters: trivial
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I34c72b9ed6c284cdd67bffea7eeac09e2c9f358f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58939
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Akash B <akash-b@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>