sctp: make use of SCTP_TRUNC4 macro

And avoid the usage of '&~3'. This is the last place still not using
the macro.
Also break the line to make it easier to read.
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/chunk.c

@@ -195,9 +195,10 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 	/* This is the biggest possible DATA chunk that can fit into
 	 * the packet
 	 */
-	max_data = (asoc->pathmtu -
-		sctp_sk(asoc->base.sk)->pf->af->net_header_len -
-		sizeof(struct sctphdr) - sizeof(struct sctp_data_chunk)) & ~3;
+	max_data = asoc->pathmtu -
+		   sctp_sk(asoc->base.sk)->pf->af->net_header_len -
+		   sizeof(struct sctphdr) - sizeof(struct sctp_data_chunk);
+	max_data = SCTP_TRUNC4(max_data);
 
 	max = asoc->frag_point;
 	/* If the the peer requested that we authenticate DATA chunks