New approach to handle peer-id related changes to link-mtu.

New approach to handle peer-id related changes to link-mtu.

Instead of statically increasing link-mtu by +3, keep the old value for
OCC compatibility with old servers/clients, and only increase link-mtu
if peer-id option is enabled (right now: is pushed by server).

If link-mtu has been set in the config, keep configured value, and log
warning (because the extra overhead has to decrease tun-mtu).

Reserve extra +3 bytes in frame->extra_link.

v2: use frame->extra_link, not frame->extra_buffer (receive path on server)
    introduce frame_add_to_link_mtu() to manipulate frame->link_mtu value
    rework comments to make more clear what is happening

This reverts commit f95010ad247a8998e0c39e394236251fca316849.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1423390725-13438-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9450