iwlwifi: mvm: rs: increase stay in column timeout

Remain in the same Tx modulation (i.e. column) for a longer
time before starting a search cycle for a better modulation.
This has been shown to give better results.
Also change the name of the timeout define to better match its
description.

Signed-off-by: Eyal Shapira <eyal@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>