MFC: r300953

MFC: r300953

1) Unifdef USE_WEAK_SEEDING it is too obsolete to support and makes reading
harder.

2) ACM paper require seed to be in [1, 2^31-2] range, so use the same range
shifting as already done for rand(3). Also protect srandomdev() + TYPE_0 case
(non default) from negative seeds.

3) Don't check for valid "type" range in setstate(), it is always valid as
calculated. Instead add a check that rear pointer not exceeed end pointer.

MFC: r300965

Micro optimize: C standard guarantees that right shift for unsigned value
fills left bits with zero, and we have exact 32bit unsigned value
(uint32_t), so there is no reason to add "& 0x7fffffff" here.

git-svn-id: svn://svn.freebsd.org/base/stable/10@301443 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f