MFC r255356:

Revert parts of r245132 and r245175. We don't need to write to the
IMAN register to clear the pending interrupt status bits. This patch
tries to solve problems seen on the MacBook Air, as reported by
Johannes Lundberg <johannes@brilliantservice.co.jp>
MFC r255483:

Do not emit size for non-regular files.  There is nothing that
mtree(1) can do in this situation and would cause confusion.
MFC r248246:

- Make quirk for reading device descriptor from broken USB devices.
Else they won't enumerate at all:
hw.usb.full_ddesc=1
- Reduce the USB descriptor read timeout from 1000ms to
500ms. Typical value for LOW speed devices is 50-100ms.
- Enumerate USB device a maximum of 3 times when a port
connection change event is detected, before giving up.
MFC r254572:
Force keyboards which don't have the required
HID fields to use the USB BOOT protocol for now.

PR:		usb/181425
MFC r255235:
  Remove unused code and sort variables declarations.

PR:		kern/181822
MFC r255472:
Clear correct data structure.
MFC of 253998:

This bug fix is in a code path in rename taken when there is a
collision between a rename and an open system call for the same
target file. Here, rename releases its vnode references, waits for
the open to finish, and then restarts by reacquiring its needed
vnode locks. In this case, rename was unlocking but failing to
release its reference to one of its held vnodes. The effect was
that even after all the actual references to the vnode had gone,
the vnode still showed active references. For files that had been
removed, their space was not reclaimed until the filesystem was
forcibly unmounted.

This bug manifested itself in the Postgres server which would
leak/lose hundreds of files per day amounting to many gigabytes of
disk space. This bug required shutting down Postgres, forcibly
unmounting its filesystem, remounting its filesystem and restarting
Postgres every few days to recover the lost space.

Reported by: Dan Thomas and Palle Girgensohn
Bug-fix by:  kib
Tested by:   Dan Thomas and Palle Girgensohn
MFC r255488:
Don't issue USB resume signalling in USB device mode, if the USB power
mode is ON and suspend is detected. This confuses iPads running in USB
host mode at least.
MFC r254742:
Hold mfi_io_lock across calls to xpt_rescan() and xpt_alloc_ccb_nowait().
xpt_rescan() expects the SIM lock to be held, and we trip a mtx_assert if
the driver initiates multiple rescans in quick succession.