iwlwifi: TX update chicken bits

This instructs FH to increment the retry count of a packet when
it is brought from the memory to TX-FIFO to save transactions
during aggregation flow.

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