net: socket: Make unnecessarily global sockfs_setattr() static

Make sockfs_setattr() static as it is not used outside of net/socket.c

This fixes the following GCC warning:
net/socket.c:534:5: warning: no previous prototype for ‘sockfs_setattr’ [-Wmissing-prototypes]

Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -533,7 +533,7 @@ static ssize_t sockfs_listxattr(struct dentry *dentry, char *buffer,
 	return used;
 }
 
-int sockfs_setattr(struct dentry *dentry, struct iattr *iattr)
+static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	int err = simple_setattr(dentry, iattr);