selftests/bpf: Implement set_hw_ring_size function to configure interface ring size

Introduce a new function called set_hw_ring_size that allows for the
dynamic configuration of the ring size within the interface.

Signed-off-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20240402114529.545475-5-tushar.vyavahare@intel.com