iwlwifi: initialize iwl_wimax_coex_cmd.flags

iwl_wimax_coex_cmd.flags can be really uninitialized, so fix
that.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>