net: skbuff.h: fix using plain integer as NULL warning

Fixes the following sparse warning:
./include/linux/skbuff.h:2365:58: warning: Using plain integer as NULL pointer

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed