Neither the SO_TIMESTAMPNS / via recvmsg() method, nor the SIOCGSTAMP / ioctl() method for obtaining the packet timestamp is supported on Windows.  This code adds a fallback to datetime, and switches to recvfrom() so that the udp_multicast bus becomes usable on windows.

on windows, the example would otherwise cause an _enter_buffered_busy fatal error, notifier shutdown and bus shutdown are racing eachother...