log when suspending a zpool
While experimenting with ZFS I/O failures, I hit a situation where the root pool would get suspended,
and due to all writes being hung (failmode=wait), the usual processing of the FMA ereport could not
make enough progress. Or perhaps it's not possible to log in to the system at all to investigate.
As it always requires some intervention to correct a suspended pool, it seems worth logging this
with CE_WARN to give an additional clue as to status.
Side note: https://illumos.org/msg/ZFS-8000-HC appears to incorrectly claim read I/Os are also suspended,
but in practice this isn't the case (and it's not just the ARC: read I/Os to the underlying device are issued and
completed). So often you can make some level of progress still until you stumble over a sync write I/O