iwlwifi: abstract out missing SEQ_RX_FRAME workaround

Mohammed Shafi ran into [1] the SEQ_RX_FRAME workaround
warning with a statistics notification, this means we
can't just remove it as we'd hoped.

Abstract it out so that the higher layer can configure
this as a kind of "filter" in the transport.

[1] http://mid.gmane.org/CAD2nsn1_DzbRHuSbS_1rFNzuux_9pW1-pABEasQ01_y7-ndO5w@mail.gmail.com

Reported-by: Mohammed Shafi <shafi.wireless@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>