selftests/xsk: print correct payload for packet dump

selftests/xsk: print correct payload for packet dump

Print the correct payload when the packet dump option is selected. The
network to host conversion was forgotten and the payload was
erronously declared to be an int instead of an unsigned int.

Fixes: facb7cb2e909 ("selftests/bpf: Xsk selftests - SKB POLL, NOPOLL")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/r/20230111093526.11682-2-magnus.karlsson@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>