net: dccp: mark expected switch fall-throughs

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

Notice that for options.c file, 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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/dccp/input.c

···
 	case DCCP_PKT_DATA:
 		if (sk->sk_state == DCCP_RESPOND)
 			break;
+		/* fall through */
 	case DCCP_PKT_DATAACK:
 	case DCCP_PKT_ACK:
 		/*

net/dccp/options.c

···
 			 * Ack vectors are processed by the TX CCID if it is
 			 * interested. The RX CCID need not parse Ack Vectors,
 			 * since it is only interested in clearing old state.
-			 * Fall through.
 			 */
+			/* fall through */
 		case DCCPO_MIN_TX_CCID_SPECIFIC ... DCCPO_MAX_TX_CCID_SPECIFIC:
 			if (ccid_hc_tx_parse_options(dp->dccps_hc_tx_ccid, sk,
 						     pkt_type, opt, value, len))