wifi: iwlwifi: mvm: validate MCC header before n_channels

wifi: iwlwifi: mvm: validate MCC header before n_channels

MCC response parsing read n_channels from v8/v4/v3 response variants
before ensuring the payload contained the fixed response header.

Add a minimum payload-length check for each response version before
reading n_channels, and keep the existing exact-size validation for the
channels array payload.

Assisted-by: GitHub Copilot:gpt-5.3-codex
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://patch.msgid.link/20260714141909.cb2cef3d3e7e.Iee7b48614289da576de842157ad3730b7589a4b1@changeid
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>