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 r261541, r261543 and r261544:
Import USB RNDIS driver to FreeBSD from OpenBSD.
Useful for so-called USB tethering.
- Imported code from OpenBSD
- Adapted code to FreeBSD
- Removed some unused functions
- Fixed some buffer encoding and decoding issues
- Optimised data transport path a bit, by sending multiple packets at a time
- Increased receive buffer to 16K

Import USB RNDIS driver to FreeBSD from OpenBSD.
Useful for so-called USB tethering.
- Imported code from OpenBSD
- Adapted code to FreeBSD
- Removed some unused functions
- Fixed some buffer encoding and decoding issues
- Optimised data transport path a bit, by sending multiple packets at a time
- Increased receive buffer to 16K

Obtained from: OpenBSD
Requested by: eadler @
MFC after: 2 weeks