Draft: CNB: xsk: Add batched buffer allocation API for the pool

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2074113
Tested: N/A

This patch set introduces a batched interface for Rx buffer allocation in AF_XDP buffer pool. Instead of using xsk_buff_alloc(*pool), drivers can now use xsk_buff_alloc_batch(*pool, **xdp_buff_array, max). Instead of returning a pointer to an xdp_buff, it returns the number of xdp_buffs it managed to allocate up to the maximum value of the max parameter in the function call. Pointers to the allocated xdp_buff:s are put in the xdp_buff_array supplied in the call. This could be a SW ring that already exists in the driver or a new structure that the driver has allocated.

Signed-off-by: Ivan Vecera ivecera@redhat.com