iwlwifi: rename CHANNEL_SWITCH_NOA_NOTIF to CHANNEL_SWITCH_START_NOTIF

There is no relation between the name and the purpose of the
notification. This notification is sent from FW when the channel switch
starts.

Signed-off-by: Nathan Errera <nathan.errera@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211024181719.24b71b0cb741.I97deb70e18f259de51395a1e7c7e58c7b006c317@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>