[CIFS] CIFS should honour umask

This patch makes CIFS honour a process' umask like other filesystems.
Of course the server is still free to munge the permissions if it wants
to; but the client will send the "right" permissions to begin with.

A few caveats:

1) It only applies to filesystems that have CAP_UNIX (aka support unix
extensions)
2) It applies the correct mode to the follow up CIFSSMBUnixSetPerms()
after remote creation

When mode to CIFS/NTFS ACL mapping is complete we can do the
same thing for that case for servers which do not
support the Unix Extensions.

Signed-off-by: Matt Keenen <matt@opcode-solutions.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>