fcc_enet multicast support.

Hello.

For quite some time set_multicast_list() is commented out in fcc_enet.c,
because it is said to be broken.
What were particular reasons to do that, i.e., where exactly is it broken?

P.S. I've seen this question in archives, but it hasn't been answered back =
then,
so I thought it's time to pose it again :)

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Regards, Wartan.