netfilter: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break statements instead of just
letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_proto_dccp.c

@@ -397,6 +397,7 @@ dccp_new(struct nf_conn *ct, const struct sk_buff *skb,
 			msg = "not picking up existing connection ";
 			goto out_invalid;
 		}
+		break;
 	case CT_DCCP_REQUEST:
 		break;
 	case CT_DCCP_INVALID:

net/netfilter/nf_tables_api.c

@@ -8557,6 +8557,7 @@ static int nf_tables_check_loops(const struct nft_ctx *ctx,
 							data->verdict.chain);
 				if (err < 0)
 					return err;
+				break;
 			default:
 				break;
 			}

net/netfilter/nft_ct.c

@@ -527,6 +527,7 @@ static void __nft_ct_set_destroy(const struct nft_ctx *ctx, struct nft_ct *priv)
 	case NFT_CT_ZONE:
 		if (--nft_ct_pcpu_template_refcnt == 0)
 			nft_ct_tmpl_put_pcpu();
+		break;
 #endif
 	default:
 		break;