ovn-controller-vtep.at: Pre-sort output before feeding to "sort -d"

ovn-controller-vtep.at: Pre-sort output before feeding to "sort -d"

NetBSD's "sort -d" preserves the order of lines which doesn't have
alphanumeric and blanks.  eg. empty lines and [].
It means it sometimes preserve unstable order of the list output.

Also, simply remove -d option where the expected output doesn't
include [].

Signed-off-by: YAMAMOTO Takashi <yamamoto@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>