iwlagn: don't resend RXON timing

Resending RXON timing here caused issues with
dual-mode under certain circumstances, so avoid
doing it here right now.

This effectively reverts b01efe434bd6ea807eb72b
and partially 2491fa42d9bdf26075765. The next
patch will make all this cleaner for just the
devices that need it.

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>