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

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

Fix up this local copy of statfoo to support > 128 statistics.

This allows all of the athstats statistics to work again.

Specifics:

* The previous code used chars < 0x80 as printable, and chars >= 0x80
as "statistics"
* .. which meant any statistic above 127 would wrap around to 0;
* .. so once I added the 802.11n TX/RX statistics to athstats, the tail
end of the statistics list weren't accessible.

This patch:

* adds a define which represents the magic character, rather than a hard
coded one
* the statistic in question is little endian encoded after the magic
character.

Notes:

* statfoo is useful enough to possibly warrant turning into a library API.

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