iwlwifi: remove HT flags from RXON when not in HT anymore

This patch removes the HT flags from RXON when moving from HT to legacy.
This avoids keeping those flags set and possibly miss configuring firmware.

If we are configured in HT, fat channel: channel 1 above, and move later
to legacy channel 11, we need to clear the FAT channel control flags in
RXON. If we don't, the firmware will understand this as channel 11 above
which is not possible due to regulatory constraints, leading to firmware
crash.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Reviewed-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>