Use P_DATA_V2 for server->client packets too

Use P_DATA_V2 for server->client packets too

P_DATA_V2 introduced the peer-id.  This allows clients to float, but as a
side-effect 32-bit aligns the encrypted data.  That alignment improves
performance particularly on cheaper/older CPUs.  So although servers don't
actually have a peer-id, still use the V2 packet format (with a zero-id)
for server->client traffic too.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1511531903-19349-1-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/search?l=mid&q=1511531903-19349-1-git-send-email-steffan.karger@fox-it.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 3b9cce657b0ba876c56ee6f14664a8a77f5b82d5)