Update README.polarssl

PolarSSL support has been extended and adjusted, but README.polarssl was
not accordingly adjusted. This updates README.polarssl to the current state
of affairs for OpenVPN 2.3.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1403640206-7024-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8804
Signed-off-by: Gert Doering <gert@greenie.muc.de>