Disable `IP_MULTICAST_ALL` sockopt => use same UDP port for all sockets
Disable `IP_MULTICAST_ALL` sockopt => use same UDP port for all sockets

Keep one socket per group, but disable the `IP_MULTICAST_ALL` sockopt so
we only receive the exact group(s) joined on a given socket, instead of
recreiving *all* groups joined on the host??  Who came up with such a
bisarre default setting?

Signed-off-by: Joachim Nilsson <583c295fd7602c168ad814279bbc3894ba65f5d6@gmail.com>

troglobit/mcjoin,troglobit/mcjoin