When the router doesn't support natpmp and PCP, one'd normally expect
the UDP packet to be ignored, and hit a time out. This logs a warning
that is already in the debug category. However, there's also the case in
which sending an UDP packet causes a ICMP response. This is returned to
user space as "connection refused" (despite UDP having no concept of
connections).
Move the warnings from `Send` and `Recv` to debug level too, to reduce
log spam in that case.
Closes#33301.
4f1a4cbccd