Cleanup DB_DNODE() macros usage

• Use the macros in few places it was missed.
• Reduce scope of DB_DNODE_ENTER/EXIT() and inline some DB_DNODE()

uses to make it more obvious what exactly is protected there and
make unprotected accesses by mistake more difficult.

• Make use of zrl_owner().

Reviewed-by: Rob Wing <rob.wing@klarasystems.com
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #16374