[Bug 1741] Enable multicast reception on each address (Windows).

[Bug 1741] Enable multicast reception on each address (Windows).
Minimize local address flip-flopping by avoiding peer_refresh_allinterfaces()
  if nothing has changed in the interface list since the last scan.
Separate handling of scope ID embedded in many in6_addr from ifindex used
  for IPv6 multicasting ioctls.
Add INT_PRIVACY endpt bit flag for IPv6 RFC 4941 privacy addresses.
Enable outbound multicast from only one address per interface in the same
  subnet, and in that case prefer embedded MAC address modified EUI-64 IPv6
  addresses first, then static, and last RFC 4941 privacy addresses.
Use setsockopt(IP[V6]_MULTICAST_IF) before each send to multicast to select
  the local source address, using the correct socket isn't enough.

bk: 4d0475a9Ar3OmzQDf-G6MvbiNEAhbA