iwlagn: set traffic load based on multiple factors

Current BT traffic load should based on the following conditions:

1. BT On/Off status
2. Channel announcement enable/disable
3. Curren traffic load report from uCode

Need to modify rate scale to down-grade from MIMO to SISO if detected
high BT traffic load. Also need to make sure not using chain "B" with high
BT traffic or if it is in "full concurrency" mode.

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