Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r253757:
Fix alignment of USB WLAN radiotap headers. This makes USB WLAN adapters
work on ARM, MIPS and similar platforms, where alignment matters.

MFC r246614:
- Streamline detach logic in wlan drivers, so that
freed memory cannot be used during detach.
- Remove all panic() calls from the urtw driver because
panic() is not appropriate here.
- Remove redundant checks for device detached in
device detach callbacks.
- Use DEVMETHOD_END to mark end of device methods.

MFC r246765:

Remove unused variable.

MFC r244503 and r246565:

Make sure all USB drivers allocate buffer memory
through the USB API and/or busdma.

The following assumptions have been made:
umass - buffers passed from CAM/SCSI layer are OK
network - mbufs are OK.

Some other nits while at it.

MFC r246944:
Fix bad EEPROM parsing code.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

s/usb2_/usb_/ on all C structs for the USB stack.

ports upgt(4) driver for USB2.