fm: pass io_flags through events & zed as uint64_t

In 4938d01db (#14086) zio_flag_t was converted from an enum (generally
signed 32-bit) to a uint64_t. The corresponding change wasn't made to
the error reporting subsystem, limiting the error flags being delivered
to zed to 32 bits. This bumps the whole pipeline to use uint64s.

A tiny bit of compatibility is added for newer zed working agsinst an
older kernel module, because its easy to do and misdetecting
scrub/resilver errors and taking action is potentially dangerous. Making
it work for new kernel modules against older zed seems to be far more
invasive for far less benefit, so I have not.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16469