ptp: use ip_mreq instead of ip_mreqn for macos
To join a multicast the MacOS still uses the interface address from the ip_mreq instead of the ip_mreqn unlike other Linux systems.
So change that join_multicast_v4 function to use ip_mreq for macos
This is similar to the fix in the glib for multicast join/leave operation on MacOS https://gitlab.gnome.org/GNOME/glib/-/merge_requests/4333