net/core/skbuff: Check the return value of skb_copy_bits()

[ Upstream commit c624c58e ]

skb_copy_bits() could fail, which requires a check on the return
value.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>