dit_init would get a skb alloc failure in dit_fill_rx_dst_data_buffer.
dit_init will check the below condition on the next call and there
will be no error.

dit_fill_rx_dst_data_buffer:
[...]
  if (initial && desc_info->dst_skb_buf[ring_num])
    return 0;
[...]

Some entries of both dst_desc and dst_skb_buf can be empty. Add a flag
to check if dst_skb_buf is filled.

Bug: 192712042
Test: Simulate skb alloc failure, then use perftest to send UDP data.

Signed-off-by: Dongseok Yi <dseok.yi@samsung.com>
Change-Id: I800971926c13fafd6a0c805844a5c443bb69c0d9
Signed-off-by: Mars Lin <marslin@google.com>