wifi: iwlwifi: mvm: don't trust firmware n_channels

In the Linux kernel, the following vulnerability has been resolved:

wifi: iwlwifi: mvm: don't trust firmware n_channels

If the firmware sends us a corrupted MCC response with n_channels much larger than the command response can be, we might copy far too much (uninitialized) memory and even crash if the n_channels is large enough to make it run out of the one page allocated for the FW response.

Fix that by checking the lengths. Doing a < comparison would be sufficient, but the firmware should be doing it correctly, so check more strictly.