selftests: net: move amt to socat for better compatibility

The test seems to expect that nc will exit after the first
received message. This is not the case with Ncat 7.94.
There are multiple versions of nc out there, switch
to socat for better compatibility.

Tell socat to exit after 128 bytes and pad the message.

Since the test sets -e make sure we don't set exit code
(|| true) and print the pass / fail rather then silently
moving over the test and just setting non-zero exit code
with no output indicating what failed.

Fixes: c08e8bae ("selftests: add amt interface selftest script")
Acked-by: Paolo <Abeni&lt;pabeni@redhat.com>
Tested-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20240509161952.3940476-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>