iwlwifi: mvm: Correctly set the tid for mcast queue

In the scheduler config command, the meaning of tid == 0xf was intended
to indicate the configuration is for management frames. However,
tid == 0xf was also used for the multicast queue that was meant only
for multicast data frames, which resulted with the FW not encrypting
multicast data frames.

As multicast frames do not have a QoS header, fix this by setting
tid == 0, to indicate that this is a data queue and not management
one.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>