move file time and dos attribute setting logic into new function

Break up cifs_setattr further by moving the logic that sets file times
and dos attributes into a separate function. This patch also refactors
the logic a bit so that when the file is already open then we go ahead
and do a SetFileInfo call. SetPathInfo seems to be unreliable when
setting times on open files.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>