wifi: nl80211: Add checks for nla_nest_start() in nl80211_send_iface()

As the nla_nest_start() may fail with NULL returned, the return value needs
to be checked.

Fixes: ce08cd34 ("wifi: nl80211: expose link information for interfaces")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20221129014211.56558-1-yuancan@huawei.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -3868,6 +3868,9 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 portid, u32 seq, int flag
 			struct cfg80211_chan_def chandef = {};
 			int ret;
 
+			if (!link)
+				goto nla_put_failure;
+
 			if (nla_put_u8(msg, NL80211_ATTR_MLO_LINK_ID, link_id))
 				goto nla_put_failure;
 			if (nla_put(msg, NL80211_ATTR_MAC, ETH_ALEN,