MFC r257543, r264912, r264972, r264982 and r266472:
- Add preliminary support for the Realtek RTL8188EUS and RTL8188ETV chipsets.
- Add device ID for 'Sanoxy 802.11N' USB
- Initialize rssi variable.
- Fix gcc build, initialize off variable.
- The DELAY() should not be used in USB drivers.
- The usb_pause_mtx() function takes ticks and not milliseconds as last argument.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Adding urtwn(4) firmware and related changes.

Reviewed by: rpaulo
Approved by: sbruno (mentor)