iwlagn: turn dynamic smps on while BT is on

While BT is on and doing iscan and/or pscan, BT is in listen
mode which will impact WiFi throughput, we need to
enable dynamic smps in order to improve the rx throughput.

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