Apple pmp patch

[mickaelifs]

This patch propose to use SOCKET_ROUTE on apple systems (as they are *BSD descendant that should be OK). It also allows nat-pmp to work correctly under MacOS platforms with VPNs that install a /1 route on the system, such a openvpn (see the def1 option of https://openvpn.net/community-resources/reference-manual-for-openvpn-2-4/). It also works the same way without VPN.