test: send an initial ping packet

test: send an initial ping packet

The hex data came from
  ping -I secnet-test-i 172.18.232.1
  tcpdump -wt -isecnet-test-i
  tcpdump -rt -x

We send it twice because the first causes a key exchange and then gets
lost.

The result is that the script crashes with
  inside rx'd!

This is because we are pinging the remote secnet, which responds
without sending the packet to its host (ie, "outside.r" in our terms).

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>