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 r246765:

Remove unused variable.
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 r238274, r246752, r256720, r256721, r256722, r256955, r257409
 r257429, r257435, r257712, r257732, r257743, r257748, r257955
 r257957, r257958, r258082, r258641, r258643, r258732, r258733,
 r258840, r258919, r258921, r259029, r259030, r259031, r259032 and r259046:

- Add support for the MediaTek/Ralink RT5370/RT5372 chipset.
- Various minor USB WLAN fixes and improvements.

PR:     usb/182936
MFC r258083:
Remove a couple of unused macros.