Disable TRIM on file backed ZFS vdevs and fix TRIM on init

After r265152 TRIM requests are ZIO_TYPE_FREE instead of ZIO_TYPE_IOCTL
this meant file backed vdevs to attempted to process the ZIO as a write
causing a panic.

We now disable TRIM on file backed vdevs and ASSERT the ZIO types supported
by each vdev type to ensure we explicity support the ZIO type being
processed.

Also ensure that TRIM on init is not procesed for devices which declare they
didn't support TRIM via vdev_notrim.

PR:		195061, 194976, 191573
Sponsored by:	Multiplay
Revert r273630 as the panic was fixed by r274619

The panic was caused by TRIM requests run against file based vdevs as write
requests.

PR:		191573
Sponsored by:	Multiplay
The "intr" option is NFS-specific; fix examples in auto_master(5).

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Mechanically replace #if defined(__FreeBSD__) and #if defined(__NetBSD__) with
their #ifdef equivalents for everything changed in contrib/netbsd-tests. There
are some items from the vendor tree that use #if defined(__FreeBSD__) or
#if defined(__NetBSD__) which are being left alone

Requested by: bde, rpaulo
Sponsored by: EMC / Isilon Storage Division
Revert r269093 which introduced physical zio alignment transform

Size of physical ZIOs must never be implicitly adjusted, it's
a responsibility of a caller to make sure that such a ZIO has proper offset
and size.

Discussed with:	delphij, gibbs
MFC after:	2 weeks
l2arc: restore correct rounding up of asize of compressed data

This rounding up was lost in a mismerge of illumos code.
See r268075 MFV r267565.
After that commit zio_compress_data() no longer performs any compressed
size adjustment, so it needs to be done externally.  On FreeBSD we round
up the size using vdev_ashift rather than SPA_MINBLOCKSIZE so that 4KB
devices are properly supported.

Additionally, zero out the buffer tail only if compression succeeds.
The compression is considered successful if the size of compressed
data after rounding up to account for the vdev ashift is less than the
original data size.  It does not make sense to have the data compressed
if all the savings are lost to rounding up.
With the new zio_compress_data() it could have been possible that the
rounded compressed size would be greater than the original size and thus
we could zero beyond the allocated buffer if the zeroing code was kept
at the original place.

Discussed with:	delphij, gibbs
MFC after:	2 weeks
X-MFC with:	r274627
Re-introduce padding fields removed with r264321 to keep
struct tcptw ABI unchanged.

Suggested by:	jhb
Approved by:	jhb (mentor)
MFC after:	1 day
X-MFC-With:	r264321
Add logic for detecting non-persistent filesystems being utilized by
workdir which would break the upgrade process upon reboot.

Currently we check for tmpfs and mdmfs.

PR:		195006
Differential Revision:	https://reviews.freebsd.org/D1163
Approved by:	cperciva
Fix geom's "usage" generation to not fabricate usage/help output for any
imaginary class we give it.

Differential Revision:	https://reviews.freebsd.org/D1150
Submitted by:	homerj
Approved by:	pjd
Clean up some language

Reviewed by:	will
Remove stray empty comment. The code is adequately explained in the
block comment above, so there's nothing to add here.