[CIFS] clean up some hard to read ifdefs

Christoph had noticed too many ifdefs in the CIFS code making it
hard to read.  This patch removes about a quarter of them from
the C files in cifs by improving a few key ifdefs in the .h files.

Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsproto.h

@@ -102,9 +102,13 @@ extern int mode_to_acl(struct inode *inode, const char *path, __u64);
 extern int cifs_mount(struct super_block *, struct cifs_sb_info *, char *,
 			const char *);
 extern int cifs_umount(struct super_block *, struct cifs_sb_info *);
-#ifdef CONFIG_CIFS_DFS_UPCALL
+#ifdef CONFIG_CIFS_DFS
 extern void dfs_shrink_umount_helper(struct vfsmount *vfsmnt);
-#endif
+#else
+static inline void dfs_shrink_umount_helper(struct vfsmount *vfsmnt)
+{
+}
+#endif /* DFS_UPCALL */
 void cifs_proc_init(void);
 void cifs_proc_clean(void);