net: gso_test: support CONFIG_MAX_SKB_FRAGS up to 45

The test allocs a single page to hold all the frag_list skbs. This
is insufficient on kernels with CONFIG_MAX_SKB_FRAGS=45, due to the
increased skb_shared_info frags[] array length.

        gso_test_func: ASSERTION FAILED at net/core/gso_test.c:210
        Expected alloc_size <= ((1UL) << 12), but
            alloc_size == 5075 (0x13d3)
            ((1UL) << 12) == 4096 (0x1000)

Simplify the logic. Just allocate a page for each frag_list skb.

Fixes: 4688ecb1

 ("net: expand skb_segment unit test with frag_list coverage")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>