Convert mcast disabled to an option bit and while doing so convert the
logic to check if multicast is enabled instead. That is make the logic
follow the option value - if it's set then mcast is enabled and vice versa.
This avoids a few confusing places where we inverted the value that's being
set to follow the mcast_disabled logic.
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com> Reviewed-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: David S. Miller <davem@davemloft.net>