The test fills the send path with up to 16 timed sends and expects one of
them to return EAGAIN. Where the loopback receive buffer can grow to
32 MiB (tcp_rmem max 33554432), 16 sends of at most 4 MiB do not fill it
and the three net_dontwait_blocking_send tests fail with "peer never
exhausted the send buffers". Raise the bound to 64; the loop still ends
at the first EAGAIN.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>