tests: fix test_1_to_1_sockopt sock buff test case

When I do the test_1_to_1_sockopt, I got a Segmentation fault:
DUMP_CORE test_1_to_1_sockopt.c: 343. I used the kernel is 3.12.

The problem is that the SOCK_MIN_SNDBUF is (TCP_SKB_MIN_TRUESIZE * 2)
while TCP_SKB_MIN_TRUESIZE is 2048 + SKB_DATA_ALIGN(sizeof(struct sk_buff))
The SKB_DATA_ALIGN I test is 256, so I make the sndbuf_val_set to 2304.

Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>