Remove use of i_sock from nbd

Signed-off-by: Matthew Wilcox <matthew@wil.cx>

Index: linux/drivers/block/nbd.c
===================================================================
RCS file: /var/cvs/linux-2.6/drivers/block/nbd.c,v
retrieving revision 1.7
diff -u -p -r1.7 nbd.c
--- linux/drivers/block/nbd.c	13 Sep 2004 15:22:55 -0000	1.7
+++ linux/drivers/block/nbd.c	19 Dec 2004 05:52:30 -0000
@@ -549,7 +549,7 @@ static int nbd_ioctl(struct inode *inode
 		file = fget(arg);
 		if (file) {
 			inode = file->f_dentry->d_inode;
-			if (inode->i_sock) {
+			if (S_ISSOCK(inode->i_mode)) {
 				lo->file = file;
 				lo->sock = SOCKET_I(inode);
 				error = 0;