[NET]: Add a dev_ioctl() fallback to sock_ioctl()

Currently all network protocols need to call dev_ioctl as the default
fallback in their ioctl implementations.  This patch adds a fallback
to dev_ioctl to sock_ioctl if the protocol returned -ENOIOCTLCMD.
This way all the procotol ioctl handlers can be simplified and we don't
need to export dev_ioctl.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index ca8b3b0..16459c7 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -1378,7 +1378,7 @@
 		}
 
  		default:
-			rc = dev_ioctl(cmd, argp);
+			rc = -ENOIOCTLCMD;
 			break;
 	}