skbuff: fix missing kernel-doc notation

Add kernel-doc notation for ndisc_nodetype:

Warning(linux-2.6.25-git2//include/linux/skbuff.h:340): No description found for parameter 'ndisc_nodetype'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -242,6 +242,7 @@ typedef unsigned char *sk_buff_data_t;
  *	@queue_mapping: Queue mapping for multiqueue devices
  *	@tc_index: Traffic control index
  *	@tc_verd: traffic control verdict
+ *	@ndisc_nodetype: router type (from link layer)
  *	@dma_cookie: a cookie to one of several possible DMA operations
  *		done by skb DMA functions
  *	@secmark: security marking