It seems multicast filtering of RTL8168F does not work.  Workaround
the silicon bug by accepting any multicast packets.

PR:	193488
MFC After:	1 week
cxgbetool: Catch up with r185979.  One of MAP_ANON, MAP_PRIVATE,
MAP_SHARED, or MAP_STACK must be specified.

This fixes the "loadfw" subcommand.

MFC after:	1 week