kernel: wifi: iwlwifi: fix iwl_mvm_max_amsdu_size() for MLO

A NULL pointer dereference vulnerability was found in the Intel iwlwifi wireless driver in the Linux kernel. When using Multi-Link Operation MLO mode, the iwlmvmmaxamsdusize function incorrectly accesses vif-bssconf.chandef.chan-band, which leads to a NULL pointer dereference because bssconf is n...