[PATCH] uml: fix net_kern workqueue abuse

Fix up the work on stack and exit scope trouble by placing the work_struct
in the uml_net_private data.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>