net: filter: mark expected switch fall-through

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

Addresses-Coverity-ID: 1472592 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -7235,6 +7235,7 @@ sk_reuseport_is_valid_access(int off, int size,
 	case offsetof(struct sk_reuseport_md, eth_protocol):
 		if (size < FIELD_SIZEOF(struct sk_buff, protocol))
 			return false;
+		/* fall through */
 	case offsetof(struct sk_reuseport_md, ip_protocol):
 	case offsetof(struct sk_reuseport_md, bind_inany):
 	case offsetof(struct sk_reuseport_md, len):