xsk: Align XDP socket batch size with DPDK

DPDK default burst size is 32, however, kernel xsk sendto
syscall can not handle all 32 at one time, and return with
error.

So make kernel XDP socket batch size larger to avoid
unnecessary syscall fail and context switch which will help
to increase performance.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/1618378752-4191-1-git-send-email-lirongqing@baidu.com