iwlwifi: enable 802.11n in Kconfig

This patch removes 'IWL4965_HT: depends on n'  from iwlwifi's Kconfig
1. 11n is functional so no need to make it invisible in the configuration
2. Latest Johannes patch 'cfg80211 API for channels/bitrates, mac80211 and
driver conversion' broke compilation because this config option was
invisible - patch fixing it will be provided later

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>