[PATCH] fix build error if CONFIG_SYSFS=n

uevent_seqnum and uevent_helper are only defined if CONFIG_HOTPLUG=y,
CONFIG_NET=n.

(I stole this back from Greg's tree - it makes allnoconfig work).

Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>