netfs: Remove extern from function prototypes

The 'extern' keyword is not necessary and removing it lets us shorten
some lines.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

include/linux/netfs.h

@@ -276,19 +276,18 @@ struct netfs_cache_ops {
 };
 
 struct readahead_control;
-extern void netfs_readahead(struct readahead_control *);
+void netfs_readahead(struct readahead_control *);
 int netfs_read_folio(struct file *, struct folio *);
-extern int netfs_write_begin(struct netfs_inode *,
-			     struct file *, struct address_space *,
-			     loff_t, unsigned int, struct folio **,
-			     void **);
-
-extern void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
-extern void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
-				 enum netfs_sreq_ref_trace what);
-extern void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
-				 bool was_async, enum netfs_sreq_ref_trace what);
-extern void netfs_stats_show(struct seq_file *);
+int netfs_write_begin(struct netfs_inode *, struct file *,
+		struct address_space *, loff_t pos, unsigned int len,
+		struct folio **, void **fsdata);
+
+void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
+void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
+			  enum netfs_sreq_ref_trace what);
+void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
+			  bool was_async, enum netfs_sreq_ref_trace what);
+void netfs_stats_show(struct seq_file *);
 
 /**
  * netfs_inode - Get the netfs inode context from the inode