hs: Cleanup logging statement in hs_intropoint.c

One log statement was a warning and has been forgotten. It is triggered for a
successful attempt at introducting from a client.

It has been reported here:
https://lists.torproject.org/pipermail/tor-relays/2017-August/012689.html



Three other log_warn() statement changed to protocol warning because they are
errors that basically can come from the network and thus triggered by anyone.

Fixes #23078.

Signed-off-by: David Goulet <dgoulet@torproject.org>