Slightly improve grammar in EAGAIN description.

PR:		176806
Submitted by:	Jeremy Chadwick
MFC after:	3 days
HYPERV isn't available on all architectures, but just on by default
for i386/amd64. Rather, it only works on i386/amd64 and should only be
built there. Rather than change the default based on which
architecutre, do things more directly by only building it on
i386/amd64 and having it always on. This is how we handle other
options that are relevant only for a few architectures.
Move the adm1030 driver to the proper location, and rename it.

For compatibility, 'device windtunnel' is still supported, but one should use
'device adm1030' instead, and this has been updated in GENERIC and NOTES.
Remove the "Unable to unwind further" message from DDB.

The ARM version of DDB is supposedly reliable enough making this
message benign.
Prevent ZFS leaking pool free space

When processing async destroys ZFS would leak space every txg timeout
(5 seconds by default), if no writes occurred, until the pool is totally
full. At this point it would be unfixable without a pool recreation.

In addition if the machine was rebooted with the pool in this situation
would fail to import on boot, hanging indefinitely, as the import process
requires the ability to write data to the pool. Any attempts to query the
pool status during the hung import would not return as the import holds
the pool lock.

The only way to import such a pool would be to specify -o readonly=on
to the zpool import.

zdb -bb <pool> can be used to check for "deferred free" size which is where
this lost space will be counted.

MFC after:	3 days
Sponsored by:	Multiplay
Add two sysctl(8) to enable/disable NFSv4 server to check when setting
user nobody and/or setting group nogroup as owner of a file or directory.
Usually at the client side, if there is an username that is not in the
client's passwd database, some clients will send 'nobody@<your.dns.domain>'
in the wire and the NFSv4 server will treat it as an ERROR.
However, if you have a valid user nobody in your passwd database,
the NFSv4 server will treat it as a NFSERR_BADOWNER as its believes the
client doesn't has the username mapped.

Submitted by:	Loic Blot <loic.blot@unix-experience.fr>
Reviewed by:	rmacklem
Approved by:	rmacklem
MFC after:	2 weeks