wifi: iwlwifi: fix max number of fw active links

The max active links that are supported by the FW is hard coded.
This is wrong since this value is HW-dependent. Fix this by
determining according to the actual HW.

Also remove a redundant check that the number of active links
doesn't exceeds the maximum.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230615094410.e78ad74c6715.I68b26911c0a312d72eaf25344b448d03b1c61f4e@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>