iwlwifi: Traffic type and counter for debugFs

Break down the traffic type and counter for both Tx and Rx.
Enhance the tx_statistics and rx_statistics debugfs function and move
to /sys/kernel/debug/ieee80211/phy0/iwlagn/debug directory to help
better debugging both driver and uCode related problems.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>