cfg80211: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

This patch fixes the following warnings:

net/wireless/wext-compat.c:1327:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
net/wireless/wext-compat.c:1341:6: warning: this statement may fall through [-Wimplicit-fallthrough=]

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling
-Wimplicit-fallthrough
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/wext-compat.c

@@ -1337,6 +1337,7 @@ static struct iw_statistics *cfg80211_wireless_stats(struct net_device *dev)
 			wstats.qual.qual = sig + 110;
 			break;
 		}
+		/* fall through */
 	case CFG80211_SIGNAL_TYPE_UNSPEC:
 		if (sinfo.filled & BIT_ULL(NL80211_STA_INFO_SIGNAL)) {
 			wstats.qual.updated |= IW_QUAL_LEVEL_UPDATED;
@@ -1345,6 +1346,7 @@ static struct iw_statistics *cfg80211_wireless_stats(struct net_device *dev)
 			wstats.qual.qual = sinfo.signal;
 			break;
 		}
+		/* fall through */
 	default:
 		wstats.qual.updated |= IW_QUAL_LEVEL_INVALID;
 		wstats.qual.updated |= IW_QUAL_QUAL_INVALID;