wifi: iwlwifi: don't spam logs with NSS>2 messages

I get a log line like this every 4 seconds when connected to my AP:

[15650.221468] iwlwifi 0000:09:00.0: Got NSS = 4 - trimming to 2

Looking at the code, this seems to be related to a hardware limitation,
and there's nothing to be done. In an effort to keep my dmesg
manageable, downgrade this error to "debug" rather than "info".

Cc: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220905172246.105383-1-Jason@zx2c4.com