templates/kfreebsd: Fix quadratic algorithm for sorting menu items

templates/kfreebsd: Fix quadratic algorithm for sorting menu items

The current implementation of the 10_kfreebsd script implements its menu
items sorting in bash with a quadratic algorithm, calling "sed", "sort",
"head", and "grep" to compare versions between individual lines, which
is annoyingly slow for kernel developers who can easily end up with
50-100 kernels in their boot partition.

This fix is ported from the 10_linux script, which has a similar
quadratic code pattern.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: debian-bsd@lists.debian.org
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>