[NETNS]: Do no include NET related headers if CONFIG_NET is not set.

This fix broken compilation for 'allnoconfig'. This was introduced by
Introduced by commit 1218854a ("[NET]
NETNS: Omit seq_net_private->net without CONFIG_NET_NS.")
Signed-off-by: NDenis V. Lunev <den@openvz.org>
Acked-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

lib/kobject_uevent.c

@@ -15,12 +15,16 @@
  */
 
 #include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+
+#ifdef CONFIG_NET
 #include <linux/socket.h>
 #include <linux/skbuff.h>
 #include <linux/netlink.h>
-#include <linux/string.h>
-#include <linux/kobject.h>
 #include <net/sock.h>
+#endif
 
 
 u64 uevent_seqnum;