Enable TCP_NODELAY configuration on FreeBSD.

The missing #include <netinet/tcp.h> causes a defined(TCP_NODELAY) to
fail.  I have added the patch to the FreeBSD ports OpenVPN 2.2.2 and
2.3.0, and confirmed (with strings ... | grep) that the TCP_NODELAY code
is now part of the executable on amd64, and results in this log output:

Sat Jan 12 13:39:18 2013 Listening for incoming TCP connection on [undef]
Sat Jan 12 13:39:18 2013 Socket flags: TCP_NODELAY=1 succeeded

Obtained from: https://community.openvpn.net/openvpn/ticket/158
Credits to: M. Nottebrock

Signed-off-by: Matthias Andree <matthias.andree@gmx.de>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: 1357994477-29981-1-git-send-email-matthias.andree@gmx.de
URL: http://article.gmane.org/gmane.network.openvpn.devel/7230
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 3e86f688757529f8b33f9e6b49e31ba8d8564c5e)