libcfnet/bwlimit: raise minimum sleep time to 1ms

After discussion with D. Apostolou, we have agreed to try with 1ms,
rather than 10μs granularity in sleeping for bandwidth throttling.

This means that "burst size" is raised to some 10kBytes for 100Mbit
networks, even 1MByte for 10Gbit/s ones.
libcfnet/bwlimit: code style improvements, types, comments

Several points, after the code revision. Still, code will act exactly
as before this commit.

Edward Welbourne wrote:
> Style: open brace on its own line, not at end of previous line.
>
> Indentation and line-splitting is odd.  Please put the && at the end
> of the previous line, so the next line's bwlimit_next lines up under
> that of the previous line, making it easier to see what they have in
> common and where they differ.  Also, the part after || should be lined
> up under the part before; if it looks to you like it does, check for
> tabs (please use spaces for indent); it doesn't appear lined up in the
> code-review !
>
> This 1000000000L is kinda hard to read.  ...
>
> next and lock can (so should) be static; they're only referenced from
> this file.


Dimitris Apostolou wrote:
> maybe you can replace the u_long type with C89/C99 type?