Account for peer-id in frame size calculation

Account for peer-id in frame size calculation

Data channel packet using P_DATA_V2 will use three bytes extra for the
peer-id. This needs to be accounted for, otherwise OpenVPN will throw

  TCP/UDP packet too large on write to [AF_INET]10.1.1.1:1194

warnings.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <1422042761-10014-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9418
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit f95010ad247a8998e0c39e394236251fca316849)