Fix SMB3.1.1 guest authentication to Samba

BugLink: http://bugs.launchpad.net/bugs/1721550

commit 23586b66 upstream.

Samba rejects SMB3.1.1 dialect (vers=3.1.1) negotiate requests from
the kernel client due to the two byte pad at the end of the negotiate
contexts.
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

fs/cifs/smb2pdu.c

@@ -418,7 +418,7 @@ assemble_neg_contexts(struct smb2_negotiate_req *req)
 	build_encrypt_ctxt((struct smb2_encryption_neg_context *)pneg_ctxt);
 	req->NegotiateContextOffset = cpu_to_le32(OFFSET_OF_NEG_CONTEXT);
 	req->NegotiateContextCount = cpu_to_le16(2);
-	inc_rfc1001_len(req, 4 + sizeof(struct smb2_preauth_neg_context) + 2
+	inc_rfc1001_len(req, 4 + sizeof(struct smb2_preauth_neg_context)
 			+ sizeof(struct smb2_encryption_neg_context)); /* calculate hash */
 }
 #else