iwlwifi: allow to switch to HT40 if not associated

iwlwifi: allow to switch to HT40 if not associated

My previous patch
6458151de53cef264648a0c4c54495852ba3253e 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>