dos: Change the DoS heartbeat line format

Fix a bug introduced in 94b56eaa which
overwrite the connection message line.

Furthermore, improve how we generate that line by using a smartlist and change
the format so it is clearer of what is being rejected/detected and, if
applicable, which option is disabled thus yielding no stats.

Closes #40308

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