ipv4: 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
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

net/ipv4/ah4.c

@@ -450,6 +450,7 @@ static int ah4_err(struct sk_buff *skb, u32 info)
 	case ICMP_DEST_UNREACH:
 		if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 			return 0;
+		break;
 	case ICMP_REDIRECT:
 		break;
 	default:

net/ipv4/esp4.c

@@ -982,6 +982,7 @@ static int esp4_err(struct sk_buff *skb, u32 info)
 	case ICMP_DEST_UNREACH:
 		if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 			return 0;
+		break;
 	case ICMP_REDIRECT:
 		break;
 	default:

net/ipv4/fib_semantics.c

@@ -1874,6 +1874,7 @@ static int call_fib_nh_notifiers(struct fib_nh *nh,
 		    (nh->fib_nh_flags & RTNH_F_DEAD))
 			return call_fib4_notifiers(dev_net(nh->fib_nh_dev),
 						   event_type, &info.info);
+		break;
 	default:
 		break;
 	}

net/ipv4/ip_vti.c

@@ -351,6 +351,7 @@ static int vti4_err(struct sk_buff *skb, u32 info)
 	case ICMP_DEST_UNREACH:
 		if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 			return 0;
+		break;
 	case ICMP_REDIRECT:
 		break;
 	default:

net/ipv4/ipcomp.c

@@ -31,6 +31,7 @@ static int ipcomp4_err(struct sk_buff *skb, u32 info)
 	case ICMP_DEST_UNREACH:
 		if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 			return 0;
+		break;
 	case ICMP_REDIRECT:
 		break;
 	default: