Fix nits in previous commit:
1.  Remove initializer for badstack_sbuf_size; it gets set unconditionally.
2.  Remove meaningless comment.
3.  Group witness_count and its sysctl together.
4.  Fix spacing in for statements (space after for and within condition).
5.  Change *all* M_NOWAIT usages in witness_initialize() to M_WAITOK; not
    just those that were newly introduced -- the allocation is assumed to
    succeed for all allocations.
6.  Avoid using uint8_t as the base type in sizeof() expressions; Use the
    variable name (w_rmatrix) as much as possible.

Pointed out by: jhb@ (thanks!)