LinuxKPI: Add sort() wrapper.

swap parameter is not supported as it is rarely used in Linux kernel
and its implementation will add some preprocessor spaghetti to qsort.

Required by drm-kmod.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D33675

(cherry picked from commit 7356f661e81d1ff88bdb4daa127f3bfa2be7ecb9)