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

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

Simplify code by changing functions types from int to avoid, as the functions
always return 0.

Found by: Clang Static Analyzer
MFC after: 1 week

Allow to checksum on-the-wire data using either CRC32 or SHA256.

MFC after: 2 weeks