linux: Make compat.linux.preserve_vstatus default to 1

From a user point of view, this makes ^T work out of the box.

Reviewed By: debdrup (man page)
Sponsored By: EPSRC
Differential Revision: https://reviews.freebsd.org/D33842

(cherry picked from commit b896bdb86d832d07ae397b340a56beb1a14ff980)