illumos gate

#14081 introduced support for EVF_VNODE mevents in bhyve, which are events that trigger when a file's metadata changes in some way. This is used to trigger resize events in various block device emulation pieces.

The FreeBSD implementation used kqueue with EVFILT_VNODE and NOTE_ATTRIB

    EVFILT_VNODE         Takes a file descriptor as the identifier and the
                         events to watch for in fflags, and returns when one
                         or more of the requested events occurs on the de-
                         scriptor.  The events to monitor are:

                         NOTE_ATTRIB          The file referenced by the de-
                                              scriptor had its attributes
                                              changed.

My illumos implementation used event ports with PORT_SOURCE_FILE and FILE_ATTRIB.
It has since become apparent that this fires for all writes to the backing file (since it watches for ctime changes)
, which is not ideal. However, most illumos bhyve VMs will be using ZFS volumes as backing storage for block
devices and, since those do not support event ports, they will be using the fallback polling method introduced in
#14374

There are tests, introduced with #14374, which check for proper operation with plain files, plain files unlinked from
the filesystem and ZFS volumes, but they failed to catch this problematic behaviour most of the time; run the plain
file test in a loop and it will eventually fail.

We should stop using event ports for this and use the polling mechanism in all cases, and also adjust the test
to properly check this.