app-layer-expectation: expectation system

app-layer-expectation: expectation system

This patch provides a working expectation system. This will allow
suricata to have a way to identify parallel connections opened by
a protocol such as FTP.

Expectation are a chained list and there is a cleaning by timeout
of the entries.

This patch also defined a counter of expectations that is also
used to check if we need to query IPPairs. This way we only query
the IPPairs store if we have an expectation.