cifs: Use help macro to get the mid header size

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2151418
commit b6b3624

It's better to use MID_HEADER_SIZE because the unfolded expression
too long. No actual functional changes, minor readability improvement.

    Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
    Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    (cherry picked from commit b6b3624)
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>

Author: Ronnie Sahlberg

fs/cifs/cifsglob.h

@@ -555,6 +555,7 @@ struct smb_version_values {
 #define HEADER_SIZE(server) (server->vals->header_size)
 #define MAX_HEADER_SIZE(server) (server->vals->max_header_size)
 #define HEADER_PREAMBLE_SIZE(server) (server->vals->header_preamble_size)
+#define MID_HEADER_SIZE(server) (HEADER_SIZE(server) - 1 - HEADER_PREAMBLE_SIZE(server))
 
 /**
  * CIFS superblock mount flags (mnt_cifs_flags) to consider when

fs/cifs/connect.c

@@ -1042,8 +1042,7 @@ standard_receive3(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 
 	/* now read the rest */
 	length = cifs_read_from_socket(server, buf + HEADER_SIZE(server) - 1,
-				       pdu_length - HEADER_SIZE(server) + 1 +
-				       HEADER_PREAMBLE_SIZE(server));
+				       pdu_length - MID_HEADER_SIZE(server));
 
 	if (length < 0)
 		return length;
@@ -1175,8 +1174,7 @@ cifs_demultiplex_thread(void *p)
 		server->pdu_size = pdu_length;
 
 		/* make sure we have enough to get to the MID */
-		if (server->pdu_size < HEADER_SIZE(server) - 1 -
-		    HEADER_PREAMBLE_SIZE(server)) {
+		if (server->pdu_size < MID_HEADER_SIZE(server)) {
 			cifs_server_dbg(VFS, "SMB response too short (%u bytes)\n",
 				 server->pdu_size);
 			cifs_reconnect(server, true);
@@ -1186,8 +1184,7 @@ cifs_demultiplex_thread(void *p)
 		/* read down to the MID */
 		length = cifs_read_from_socket(server,
 			     buf + HEADER_PREAMBLE_SIZE(server),
-			     HEADER_SIZE(server) - 1 -
-			     HEADER_PREAMBLE_SIZE(server));
+			     MID_HEADER_SIZE(server));
 		if (length < 0)
 			continue;
 		server->total_read += length;