iwlwifi: mvm: handle FIF_ALLMULTI when setting multicast addresses

We were ignoring the FIF_ALLMULTI flag when setting the multicast
addresses with MCAST_FILTER_CMD.  Check if this flag is set and enable
pass_all accordingly.  We also need to set the count to 0 if pass_all
is enable so we don't pass addresses to the firmware when not needed
(as doing so causes an assert).

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=196741



Signed-off-by: Luca Coelho <luciano.coelho@intel.com>