BUG/MINOR: tcpcheck: Report hexstring instead of binary one on check failure

BUG/MINOR: tcpcheck: Report hexstring instead of binary one on check failure

When an expect rule failed for a tcp-check, information about the expect
rule is dumped in the report. For a check on a binary string, a hexstring is
used in the configuration but the decoded string is dumped. It is an problem
because it can contain special characters. And it is not really handy
because there is no correspondance with the config.

So, now, the hexstring is dumped in the report. This way, we are sure there
is no special characters and it is easy to find it in the configuration.

This patch shoudl solve the issue #2326. It must be backported as far as
2.2.