ipv6: mark expected switch fall-throughs

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

Notice that in some cases I placed the "fall through" comment
on its own line, which is what GCC is expecting to find.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index e4462b0..761a473 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -1055,6 +1055,7 @@ static int rawv6_setsockopt(struct sock *sk, int level, int optname,
 		if (optname == IPV6_CHECKSUM ||
 		    optname == IPV6_HDRINCL)
 			break;
+		/* fall through */
 	default:
 		return ipv6_setsockopt(sk, level, optname, optval, optlen);
 	}
@@ -1077,6 +1078,7 @@ static int compat_rawv6_setsockopt(struct sock *sk, int level, int optname,
 		if (optname == IPV6_CHECKSUM ||
 		    optname == IPV6_HDRINCL)
 			break;
+		/* fall through */
 	default:
 		return compat_ipv6_setsockopt(sk, level, optname,
 					      optval, optlen);
@@ -1138,6 +1140,7 @@ static int rawv6_getsockopt(struct sock *sk, int level, int optname,
 		if (optname == IPV6_CHECKSUM ||
 		    optname == IPV6_HDRINCL)
 			break;
+		/* fall through */
 	default:
 		return ipv6_getsockopt(sk, level, optname, optval, optlen);
 	}
@@ -1160,6 +1163,7 @@ static int compat_rawv6_getsockopt(struct sock *sk, int level, int optname,
 		if (optname == IPV6_CHECKSUM ||
 		    optname == IPV6_HDRINCL)
 			break;
+		/* fall through */
 	default:
 		return compat_ipv6_getsockopt(sk, level, optname,
 					      optval, optlen);