selftests/xsk: dump packet at error

Dump the content of the packet when a test finds that packets are
received out of order, the length is wrong, or some other packet
error. Use the already existing pkt_dump function for this and call it
when the above errors are detected. Get rid of the command line option
for dumping packets as it is not useful to print out thousands of
good packets followed by the faulty one you would like to see.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20230516103109.3066-5-magnus.karlsson@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>