iwlagn: fix minimum number of queues setting

We need to provide a reasonable minimum that will result in a
working setup if used. Set minimum to be 10 to provide for
4 standard TX queues + 1 command queue + 2 (unused) HCCA queues +
4 HT queues (one per AC).

We allow the user to change the number of queues used via a module
parameter and use this minimum value to check if it is valid. Without
this patch a user can select a value for the number of queues that
will result in a failing setup.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>