IPsec: Allow to create on-demand connections

IPsec: Allow to create on-demand connections

This will create IPsec VPN connections with auto=route set
instead of auto=start which will cause the connection being
created, but not brought up yet.

As soon as the first packet is received, the connection will
be established and data will be passed through it.

This allows IPFire to handle more VPN connections on weaker
systems and avoids negotiating many connections which are
rarely used.

Suggested-by: Tom Rymes <tomvend@rymes.com>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Fixes: #10733