iwlwifi: allow to switch to HT40 if not associated

iwlwifi: allow to switch to HT40 if not associated

My previous patch
54eb1ded490dc052d8d608ed829aea157b40a2ac iwlwifi: do not re-configure
HT40 after associated

Fix the case of HT40 after association on specified AP, but it break the
association for some APs and cause not able to establish connection.
We need to address HT40 before and after addociation.

CC: stable@vger.kernel.org #3.0+
Reported-by: Andrej Gelenberg <andrej.gelenberg@udo.edu>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Tested-by: Andrej Gelenberg <andrej.gelenberg@udo.edu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>