iwlwifi: mvm: fix kernel panic in case of assert during CSA

During CSA, we briefly nullify the phy context, in __iwl_mvm_unassign_vif_chanctx.
In case we have a FW assert right after it, it remains NULL though.
We end up running into endless loop due to mac80211 trying repeatedly to
move us to ASSOC state, and we keep returning -EINVAL. Later down the road
we hit a kernel panic.

Detect and avoid this endless loop.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201107104557.d64de2c17bff.Iedd0d2afa20a2aacba5259a5cae31cb3a119a4eb@changeid

Author: sara-s

drivers/net/wireless/intel/iwlwifi/mvm/mac80211.c

@@ -3080,7 +3080,7 @@ static int iwl_mvm_mac_sta_state(struct ieee80211_hw *hw,
 
 	/* this would be a mac80211 bug ... but don't crash */
 	if (WARN_ON_ONCE(!mvmvif->phy_ctxt))
-		return -EINVAL;
+		return test_bit(IWL_MVM_STATUS_HW_RESTART_REQUESTED, &mvm->status) ? 0 : -EINVAL;
 
 	/*
 	 * If we are in a STA removal flow and in DQA mode: