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

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

Update iwn(4) firmware blobs:
- bump iwn1000fw to 39.31.5.1
- bump iwn5000fw to 8.83.5.1
- bump iwn6050fw to 41.28.5.1

- Update 6000 firmware to 9.221.4.1
- Add 6050 firmware

MFC after: 2 weeks