mbedtls: include correct net/net_sockets header according to version

mbedtls: include correct net/net_sockets header according to version

<mbedtls/net.h> is deprecated as of mbedTLS 2.4.0, it is renamed
<mbedtls/net_sockets.h>. OpenVPN will fail to build with
mbedTLS 2.4.0 with MBEDTLS_DEPRECATED_REMOVED defined.

Check MBEDTLS_VERSION_NUMBER, and include net.h for < 2.4.0 and
net_sockets.h for >= 2.4.0.

Signed-off-by: Magnus Kroken <mkroken@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1481274455-657-1-git-send-email-mkroken@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13451.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>