Adapt socket handling to support listening on multiple sockets

Adapt socket handling to support listening on multiple sockets

    Introduce internal changes preparing the server to
    handle multiple sockets concurrently for both
    TCP and UDP protocols. While no user-visible
    features are implemented yet, these modifications
    are essential for enabling future functionality
    such as listening on multiple ports.

    Key changes are: converting link_socket from a
    single pointer to an array in various contexts,
    in order to be able to store multiple sockets
    at once.

Change-Id: Ia0a889e800f0b36aed770ee36e31afeec5df6084
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Gianmarco De Gregori <gianmarco@mandelbit.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20241230162338.21401-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30309.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>