uml: Replace one-element array with zero-element array

To look at users I did:
$ find arch/um/ include/asm-um -name '*.[ch]'|xargs grep -r 'net_kern\.h'
+-l|xargs grep '\<user\>'

Most users just cast user to the appropriate pointer, the remaining ones are
fixed here.  In net_kern.c, I'm almost sure that save trick is not needed
anymore, but I've not verified it.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/include/net_kern.h b/arch/um/include/net_kern.h
index 125ab42..9237056 100644
--- a/arch/um/include/net_kern.h
+++ b/arch/um/include/net_kern.h
@@ -40,7 +40,7 @@
 	void (*add_address)(unsigned char *, unsigned char *, void *);
 	void (*delete_address)(unsigned char *, unsigned char *, void *);
 	int (*set_mtu)(int mtu, void *);
-	int user[1];
+	char user[0];
 };
 
 struct net_kern_info {