selftests/xsk: do not change XDP program when not necessary

Do not change the XDP program for the Tx thread when not needed. It
was erroneously compared to the XDP program for the Rx thread, which
is always going to be different, which meant that the code made
unnecessary switches to the same program it had before. This did not
affect functionality, just performance.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20230516103109.3066-2-magnus.karlsson@gmail.com


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