iwlwifi: Demote messages about fw flags size to info

These messages are not reporting a real error, just the fact that the
firmware knows about more flags than the driver.

Currently these messages are presented to the user during boot if there
is no bootsplash covering the console, even when booting the kernel with
"quiet".

Demoting it to the warn level helps having a clean boot process.

Signed-off-by: João Paulo Rechi Vita <jprvita@endlessm.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>