multicast: remove useless parameter for group add

Remove the mode parameter for igmp/igmp6_group_added as we can get it
from first parameter.

Fixes: 6e2059b5 (ipv4/igmp: init group mode as INCLUDE when join source group)
Fixes: c7ea20c9

 (ipv6/mcast: init as INCLUDE when join SSM INCLUDE group)
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>