bpf: fix return in bpf_skb_adjust_net

The bpf_skb_adjust_net() ignores the return value of bpf_skb_net_shrink/grow,
and always return 0, fix it by return 'ret'.
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -2248,7 +2248,7 @@ static int bpf_skb_adjust_net(struct sk_buff *skb, s32 len_diff)
 		       bpf_skb_net_grow(skb, len_diff_abs);
 
 	bpf_compute_data_end(skb);
-	return 0;
+	return ret;
 }
 
 BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,