net/af_xdp: allow bigger batch sizes

net/af_xdp: allow bigger batch sizes

Prior to this commit, the maximum batch sizes for zero-copy and
copy-mode rx and copy-mode tx were set to 32. Apart from zero-copy tx,
the user could never rx/tx any more than 32 packets at a time and
without inspecting the code the user wouldn't be aware of this.

This commit removes these upper limits placed on the user and instead
sets an internal batch size equal to the default ring size (2048).
Batches larger than this are still processed, however they are split
into smaller batches similar to how it's done in other drivers. This is
necessary because some arrays used during rx/tx need to be sized at
compile-time.

Allowing a larger batch size allows for fewer batches and thus larger
bulk operations, fewer ring accesses and fewer syscalls which should
yield improved performance.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>