security/strongswan: Fix default control-interface

Fix default control-interface in rc.d script and also
make it user-selectable at build time, defaulting to VICI.

Also mention this change in pkg-message, as previously the
default was "stroke" and it was changed to "vici" with
only a short notice in UPDATING, that was not displayed
when using binary upgrades.

Committing a portfmt'd version.

PR: 255952
Approved by: strongswan@Nanoteq.com (maintainer)