SMB3: Work around mount failure when using SMB3 dialect to Macs

SMB3: Work around mount failure when using SMB3 dialect to Macs

commit 7db0a6efdc3e990cdfd4b24820d010e9eb7890ad upstream.

Macs send the maximum buffer size in response on ioctl to validate
negotiate security information, which causes us to fail the mount
as the response buffer is larger than the expected response.

Changed ioctl response processing to allow for padding of validate
negotiate ioctl response and limit the maximum response size to
maximum buffer size.

Signed-off-by: Steve French <steve.french@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>