[ Upstream commit f1640c3d ]

when build_skb failed, it may occure a NULL pointer.
So add a 'NULL check' for it.
Signed-off-by: Weidong Wang <wangweidong1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>