selftests/bpf: Fix test_lirc test

Since commit 68a99f6a0ebf ("media: lirc: report ir receiver overflow"),
the rc-loopback driver does not accept edges over 50ms, as these are
never seen in real life ir protocols. Fix this.

Signed-off-by: Sean Young <sean@mess.org>
Link: https://lore.kernel.org/r/20260605151417.777614-1-sean@mess.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>