Rename 'struct route' to 'struct route_ipv4'

To fix trac #340, we need to rename our "struct route" to avoid a
collision with "struct route" from <net/route.h> on *BSD.

No functional changes.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1389650074-18455-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8231
(cherry picked from commit b57e005b8f232760081875937a53e8e7d235faa6)
Replace copied structure elements with including <net/route.h>

The code for FreeBSD, Dragonfly, OpenBSD and NetBSD contained copies
of structures from <net/route.h> (struct rt_msghdr in particular).

OpenBSD changed some structure elements, making OpenVPN incompatible,
depending on the specific OpenBSD version.  Clean up: remove copied
definitions, replace by including <net/route.h> directly - this could
not be done originally due to a conflict with "struct route" in OpenVPN
and <net/route.h>, cleaned up by the previous commit.

Tested on FreeBSD 9.1-RELEASE, NetBSD 5.1, OpenBSD 4.9 (route.c compiles
with no warnings, and "openvpn --show-gateway" works, which is the only
part of the code that uses the structures in question).

Fix trac #340

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1389650074-18455-2-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8230
(cherry picked from commit 615fb9ef36310f85fd6171301128a12740444455)