In my eagerness to eliminate a branch which is taken once per 2^38
bytes of keystream, I forgot that the state words are in host order.
Thus, the counter increment code worked fine on little-endian
machines, but not on big-endian ones. Switch to a simpler (branchful)
solution.
numbers with Chacha20. Keep the API, though, as that is what the
other *BSD's have done.
Use the boot-time entropy stash (if present) to bootstrap the
in-kernel entropy source.
Reviewed by: delphij,rwatson
Approved by: so(delphij)
MFC after: 2 months
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D10048
