CIFS: Implement cifs_file_strict_mmap (try #2)

Invalidate inode mapping if we don't have at least Level II oplock.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsfs.h

@@ -89,6 +89,7 @@ extern int cifs_fsync(struct file *, int);
 extern int cifs_strict_fsync(struct file *, int);
 extern int cifs_flush(struct file *, fl_owner_t id);
 extern int cifs_file_mmap(struct file * , struct vm_area_struct *);
+extern int cifs_file_strict_mmap(struct file * , struct vm_area_struct *);
 extern const struct file_operations cifs_dir_ops;
 extern int cifs_dir_open(struct inode *inode, struct file *file);
 extern int cifs_readdir(struct file *file, void *direntry, filldir_t filldir);